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`Vol. 332 No. 14
`
`EDITORIALS
`
`951
`
`PARADIGMATIC SHIFTS IN THE
`MANAGEMENT OF BREAST CANCER
`
` has been almost exactly 100 years since William
`I
`T
`Halsted published his seminal report on the use of rad-
`ical mastectomy “for the cure of cancer of the breast,”
`1
`and it is fitting that this issue of the
` includes
`Journal
`the long-term results of two randomized trials evaluat-
`ing treatment for breast cancer that might be cured
` Halsted’s ideas and his oper-
`with mastectomy alone.
`2,3
`ation dominated our thinking about the treatment of
`breast cancer until approximately 25 years ago, when a
`major paradigmatic shift began. The premises underly-
`ing the Halsted approach were that metastases oc-
`curred by centrifugal and contiguous spread from the
`primary tumor in the breast and that, as a result, im-
`proved local control should decrease the frequency of
`metastases and death from cancer.
` In his first report,
`4
`Halsted stated that an operation should be judged on
`the achievement of local control rather than “ultimate
`cure.” Thus, subsequent generations of physicians have
`rejected the use of any local treatment associated with
`a rate of local recurrence higher than that achieved
`with radical mastectomy.
`1
`Six randomized trials have demonstrated that the
`survival of patients treated with a breast-conserving
`operation (variously referred to as lumpectomy, tylecto-
`my, wide excision, or quadrantectomy) plus radiothera-
`py is equivalent to that of patients treated with mastec-
`tomy.
` However, the same degree of local control is not
`2
`always achieved with these two procedures. In the
`study by Jacobson et al. reported in this issue of the
` 18 percent of patients had a recurrence within
`2
`Journal,
`the irradiated breast; 5 percent of the patients receiv-
`ing the breast-conserving treatment had a local or re-
`gional recurrence — that is, one involving regional
`lymph nodes, skin, or muscle — or could not undergo
`surgery for some other reason at the time of recur-
`rence. Of course, none of the patients in the mastecto-
`my group had a recurrence within the breast, but 10
`percent had a local or regional recurrence. In general,
`a local recurrence after mastectomy has about the
`same prognostic importance as a distant recurrence,
`5
`and it is often assumed that a recurrence within the
`breast after irradiation has the same implication as any
`other type of local or regional recurrence. The fact that
`the overall survival of patients randomly assigned to
`receive breast-conserving therapy and radiation thera-
`py in these studies is equivalent to the survival of pa-
`tients who underwent mastectomy in spite of the higher
`local-failure rate suggests that recurrences confined to
`the irradiated breast do not have the same prognostic
`importance as recurrences in the lymph nodes, skin,
`and muscle. Another possibility is that the rate of local
`recurrence is not a good surrogate end point for surviv-
`al, as assumed by Halsted and his successors.
`The use of breast-conserving operations and radio-
`therapy does not, however, represent a paradigmatic
`shift. If anything, this form of local treatment is more
`extensive (or more radical), because the supraclavicu-
`
`lar and internal mammary nodes are treated more ef-
`fectively with radiation than they are with even the
`most radical forms of surgery. For a true evaluation of
`Halsted’s hypothesis, patients in several studies have
`been randomly assigned to receive breast-conserving
`therapy alone or with radiotherapy.
` In these studies
`6-8
`too, a higher local-recurrence rate among women who
`underwent lumpectomy alone did not compromise sur-
`vival. However, a recent reanalysis of one of these stud-
`ies suggests that this finding may not hold true with fol-
`low-up periods of more than 10 years.
` Local failure is
`9
`a particularly difficult consequence of therapy for most
`patients because it is readily apparent and is thus a
`constant reminder that the tumor is no longer curable.
`For both these reasons, the importance of local control
`cannot be dismissed as entirely irrelevant.
`3
`The first reports describing an improvement in dis-
`ease-free survival with the use of adjuvant chemother-
`apy also stimulated intense controversy.
` Many ar-
`10,11
`gued that an improvement in disease-free survival
`would not necessarily lead to an improvement in over-
`all survival, that early results would not necessarily be
`confirmed with longer follow-up, and that this research
`was “diverting the funds away from more valuable bas-
`ic research.”
` However, the results with adjuvant che-
`12
`motherapy have been confirmed in additional studies
` The report
`and in an overview of all adjuvant studies.
`13
`by Bonadonna and his colleagues in this issue of the
` demonstrates that the effects are lasting.
`3
`Journal
`The underlying rationale for the use of systemic
`therapy as an adjuvant to surgery is that patients die
`despite the achievement of good local control because
`blood-borne micrometastases are present in distant or-
`gans long before the diagnosis of breast cancer can be
`made with the most sensitive techniques now avail-
` This clearly represents a shift from the views of
`able.
`14
`Halsted and other surgeons of the 19th and early 20th
`centuries. The results of these adjuvant-chemotherapy
`trials provide substantial evidence, if not proof, that
`this new concept is correct and is much more impor-
`tant than the relatively small survival benefit that is
`achieved, because it indicates that further improve-
`ment in the survival of patients with breast cancer
`will be achieved by better systemic rather than local
`therapy.
`Are some patients cured by adjuvant treatment
`whereas others derive no benefit at all? Or is the sur-
`vival of most patients prolonged only transiently, with
`no patients or very few cured?
` Adjuvant-chemothera-
`15
`py trials do not provide much insight into these ques-
`tions. The curves shown in Figure 1 of the article by
` could be used to support either one
`Bonadonna et al.
`3
`of these interpretations. However, the latter explana-
`tion seems more probable. At the time of the analysis,
`138 of the 179 patients randomly assigned to the con-
`trol group had died, but only 10 of these women (7 per-
`cent) died without evidence of disease recurrence.
` Of
`3
`the 207 women randomly assigned to receive adjuvant
`chemotherapy, 137 had died, but only 14 (10 percent)
`died without evidence of disease recurrence (P not sig-
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
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`
`952
`
`THE NEW ENGLAND JOURNAL OF MEDICINE
`
`April 6, 1995
`
`nificant). These findings suggest that the percentage of
`women who died of breast cancer in the two groups was
`nearly the same but that the time at which they died
`was different. To some women, especially those with a
`good prognosis, it is important to know whether ad-
`juvant therapy will prolong their lives rather than erad-
`icate the disease and, if so, how much their lives will
`be prolonged.
` Unfortunately, even after 25 years of
`15
`study, we can only roughly estimate the additional
`months or years of life that any one patient might gain
`as a result of this treatment.
`The benefits of adjuvant chemotherapy may result
`from a direct cytotoxic effect of the therapy on the can-
`cer cells, as is most often presumed, or from an indirect
`effect mediated by an endocrine organ such as the ova-
`ry. These effects are not mutually exclusive. It is strik-
`ing that in almost all individual studies and in an over-
`view of all adjuvant-chemotherapy trials, the beneficial
`effects of adjuvant chemotherapy are smaller among
`postmenopausal women than premenopausal women.
`13
`Bonadonna and his colleagues argue that this differ-
`ence arises from the use of reduced doses of chemother-
`apy in older women.
` In addition, they reason that if the
`3
`effects of adjuvant chemotherapy are the result of a
`chemical ovarian ablation, the reduction in mortality
`produced by chemotherapy should be greater among
`premenopausal women with drug-induced amenorrhea
`than among treated premenopausal women who did not
`become amenorrheic. This was not observed. Theirs is
`not the last word on this subject, however. A better ex-
`periment would be a randomized comparison of ovari-
`an ablation with chemotherapy in premenopausal wom-
`en. One such study has recently been reported, and it
`failed to show a significant difference in outcome relat-
`ed to the treatment used.
`
`16
`The importance of this question lies in the research
`paths we pursue in the next decade. If, in fact, the sur-
`vival benefits of chemotherapy are primarily a result of
`ovarian ablation, then therapy involving manipulation
`of the dozens of newly identified growth factors is par-
`ticularly promising. On the other hand, if the survival
`benefits result primarily from the direct cytotoxic ef-
`fects of the drugs, then very-high-dose chemotherapy
`and other strategies that circumvent the rapid resist-
`ance that develops to chemotherapy hold greater
`promise.
`In both these papers possibly the most important
`point, which should not be overlooked, is the survival
`of patients in all treatment groups after 10 to 20 years
`of follow-up. In the study from Milan,
` which included
`3
`only patients with histologically positive lymph nodes,
`
`25 percent of the patients treated with mastectomy
`alone and 34 percent of the patients who received ad-
`juvant chemotherapy were still alive at 20 years. The
` included a
`study from the National Cancer Institute
`2
`number of patients with a better prognosis; the 10-year
`survival of all patients exceeded 70 percent. These data
`should be reassuring to the many patients with cancer
`who believe that a diagnosis of breast cancer is a death
`sentence. Taken together, these numbers also demon-
`strate that many patients survive for long periods with
`local therapy only and presumably, at least in part, as
`a result of that therapy. Adjuvant chemotherapy pro-
`longs the survival of other patients.
`
`University of California,
`San Francisco
`San Francisco, CA 94143
`
`I. C
`
`RAIG
`
` H
`
`ENDERSON
`
`, M.D.
`
`R
`
`EFERENCES
`
`1. Halsted WS. The results of operations for the cure of cancer of the breast
`performed at the Johns Hopkins Hospital from June 1889 to January 1894.
`Johns Hopkins Hosp Rep 1894;4:297-350.
`2. Jacobson JA, Danforth DN, Cowan KH, et al. Ten-year results of a compar-
`ison of conservation with mastectomy in the treatment of stage I and II
`breast cancer. N Engl J Med 1995;332:907-11.
`3. Bonadonna G, Valagussa P, Moliterni A, Zambetti M, Brambilla C. Adjuvant
`cyclophosphamide, methotrexate, and fluorouracil in node-positive breast
`cancer — the results of 20 years of follow-up. N Engl J Med 1995;332:901-6.
`4. Halsted WS. The results of radical operations for the cure of carcinoma of
`the breast. Ann Surg 1907;46:1-19.
`5. Bruce J, Carter DC, Fraser J. Patterns of recurrent disease in breast cancer.
`Lancet 1970;1:433-5.
`6. Fisher B, Anderson S, Fisher ER, et al. Significance of ipsilateral breast tu-
`mour recurrence after lumpectomy. Lancet 1991;338:327-31.
`7. Veronesi U, Luini A, Del Vecchio M, et al. Radiotherapy after breast-pre-
`serving surgery in women with localized cancer of the breast. N Engl J Med
`1993;328:1587-91.
`8. Liljegren G, Holmberg L, Adami HO, Westman G, Graffman S, Bergh J.
`Sector resection with or without postoperative radiotherapy for stage I breast
`cancer: five-year results of a randomized trial. J Natl Cancer Inst 1994;86:
`717-22.
`9. Stablein DM. Final report of a reanalysis of NSABP Protocol B06. Cancer-
`Fax from the National Cancer Institute. ID #400028. Prepared by the
`EMMES Corporation, June 1, 1994.
`10. Fisher B, Carbone P, Economou SG, et al. l-Phenylalanine mustard (L-PAM)
`in the management of primary breast cancer: a report of early findings.
`N Engl J Med 1975;292:117-22.
`11. Bonadonna G, Brusamolino E, Valagussa P, et al. Combination chemother-
`apy as an adjuvant treatment in operable breast cancer. N Engl J Med 1976;
`294:405-10.
`12. Rodriguez-Antunez A. The triumphalistic oncologist. Surg Gynecol Obstet
`1978;146:617-8.
`13. Early Breast Cancer Trialists’ Collaborative Group. Systemic treatment of
`early breast cancer by hormonal, cytotoxic, or immune therapy: 133 ran-
`domised trials involving 31 000 recurrences and 24 000 deaths among
`75 000 women. Lancet 1992;339:1-15, 71-85.
`14. Fisher B. The evolution of paradigms for the management of breast cancer:
`a personal perspective. Cancer Res 1992;52:2371-83.
`15. Henderson IC. The nature of the benefit. In: Henderson IC, ed. Adjuvant
`therapy of breast cancer. Boston: Kluwer Academic, 1992:57-68.
`16. Scottish Cancer Trials Breast Group ICRF Breast Unit, Guy’s Hospital, Lon-
`don. Adjuvant ovarian ablation versus CMF chemotherapy in premenopausal
`women with pathological stage II breast carcinoma: the Scottish trial. Lancet
`1993;341:1293-8.
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
`Apotex Tech.
`Ex. 2023
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`Vol. 332 No. 14
`
`EDITORIALS
`
`953
`
`AN ORALLY ACTIVE IRON CHELATOR
`
` is essential for all organisms from bacteria to
`I
`RON
`humans; but like excessive amounts of alcohol, which is
`so pleasant in moderation, a surfeit of iron is fatal. The
`lethal effects of iron overload can be immediate, as in
`an accidental or deliberate overdose of medicinal iron,
`or slow, as in congenital hemochromatosis and transfu-
`sional hemosiderosis. In the slowly developing condi-
`tions — the former due to hyperabsorption of iron in
`food and the latter to iatrogenic, as well as, in the case
`of thalassemia, hyperabsorptive factors — iron stores
`in the reticuloendothelial system are filled to the brim
`with nontoxic ferruginous granules. Spillage of iron
`into parenchyma and plasma is inevitable, and toxic ef-
`fects due to oxidation of membranes follow. The excess
`iron saturates the binding sites of transferrin, the “de-
`livery boy” of iron metabolism, allowing free iron to cir-
`culate and oxidize heart-muscle membranes
` until the
`1
`patient succumbs to heart failure and arrhythmia.
`Thalassemia is one of the most common diseases in
`regions of the world where malaria has long been ram-
`pant. This inherited disorder of hemoglobin synthesis is
`fatal in infancy without transfusions but is fatal in ado-
`lescence even with them. The advent of treatment with
`subcutaneous deferoxamine has changed this gloomy
`prognosis. Recent studies demonstrate that over 90
`percent of patients who comply with the difficult and
`expensive regimen of deferoxamine treatment survive
`without heart disease
` and with minimal toxic effects if
`2
`the dose is tailored to the iron burden.
`3
`Deferoxamine has a very high and selective affinity
`for iron that is independent of the iron concentration.
`4
`The required dose is relatively low (about 40 to 50 mg
`per kilogram of body weight administered in an over-
`night subcutaneous infusion). Serious side effects are
`rare. But the drug is not active orally, and nightly sub-
`cutaneous self-administration is onerous, leading to a
`high frequency of noncompliance, a uniformly fatal
`“complication” of therapy.
`There are only two alternatives to subcutaneous de-
`feroxamine: allogeneic bone marrow transplantation
`for the 25 percent of patients with histocompatible do-
`nors, and an orally active iron chelator. The former has
`received attention recently because of a report from a
`center in Italy, where patients with good chelation had
`more than a 90 percent likelihood of indefinite thalas-
`semia-free survival after bone marrow transplantation.
`5
`However, the investigators’ method of stratifying pa-
`tients is not readily reproducible, and experience with
`bone marrow transplantation in young patients with
`good chelation in the United Kingdom and the United
`States shows that the rate of disease-free survival is no
`higher than 75 percent and may be lower.
` Neverthe-
`6,7
`less, bone marrow transplantation can solve the thera-
`peutic problem once and for all and, until now, has
`been the only useful option if a patient cannot or will
`not use deferoxamine or if the blood supply is of uncer-
`tain safety and reliability.
`In this issue of the
` Olivieri and her colleagues
`Journal,
`report a clinical trial of the new, orally active agent
` De-
`deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one).
`8
`
`feriprone has a checkered history. It was originally
`synthesized by Robert Hider and his colleagues at Es-
`sex University, and the early biologic assessments were
`performed at University College Hospital in London.
`9
`The drug was used in the clinic of another London
`hospital without sufficient studies of toxic effects in an-
`imals and without Hider’s approval.
`Deferiprone has a much lower therapeutic ratio
`than deferoxamine, for two reasons. First, deferiprone
`is considerably more toxic and regularly depresses the
`granulocyte count in both normal and iron-overloaded
`animals
`; deferoxamine, in contrast, does not depress
`10
`the marrow. In clinical studies, deferiprone has caused
`both agranulocytosis and arthralgia or arthritis; the
`frequency of these complications is not yet known.
`Second, though Olivieri and her colleagues clearly
`demonstrate that deferiprone can reduce iron stores to
`lower, if still elevated, levels in patients with severe
`overload, the drug has a concentration-dependent af-
`finity for iron.
` Three molecules of deferiprone are re-
`4
`quired to bind one molecule of iron, whereas deferox-
`amine binds iron tightly in a 1:1 ratio. For this reason,
`deferiprone must be present at very high concentra-
`tions (close to toxic levels) to be effective. It dissociates
`from iron when the concentration of iron in body fluids
`falls to the level achieved just a few hours after oral ad-
` Hence, as demonstrated by Olivieri and
`ministration.
`4
`her colleagues, deferiprone does not readily reduce ex-
`cessive body iron stores below a certain level. It is
`therefore not clear that the drug will provide long-
`term protection from heart disease.
`Not enough is known about the pharmacologic
`properties of deferiprone. Will the low levels of drug
`that remain in the plasma continue to chelate free iron
`and thereby protect heart-muscle membranes, or will
`the small but highly toxic pool of free iron remain or
`return to high levels between doses to do its damage?
`Over time, will the drug’s ability to be absorbed prove
`to be a two-edged sword because it can also permeate
`the cell membranes of vital organs such as the kidney,
`with toxic effects? That has been the sad fate of an
`extremely active oral iron chelator called desferithio-
`cin.
` Finally, will adolescents really swallow enough
`11
`pills to amount to 75 mg per kilogram in three divided
`doses every day? For an adolescent of average weight,
`this represents 1 to 2 g of the drug three times daily.
`Such a burdensome regimen is itself an open invitation
`to noncompliance and the development of heart dis-
`ease. Ominously, 10 percent of the patients in the trial
`reported by Olivieri et al. did not comply with the
`regimen.
`Given these concerns, clinical studies of deferiprone
`that last for several years and enroll at least 100 pa-
`tients will be required before physicians can advise pa-
`tients with thalassemia to dispense with nightly subcu-
`taneous administration of deferoxamine and instead
`swallow a handful of capsules every eight hours. Pa-
`tients who are unable or unwilling to use deferoxamine
`and for whom there are histocompatible donors avail-
`able will have to weigh the unknown risks of defer-
`iprone against the more established risks of bone mar-
`row transplantation.
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
`Apotex Tech.
`Ex. 2023
`
`

`

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`
`954
`
`THE NEW ENGLAND JOURNAL OF MEDICINE
`
`April 6, 1995
`
`Despite questions about the long-term efficacy and
`safety of deferiprone in the management of thalasse-
`mia, Olivieri and her coworkers are to be congratulat-
`ed for rescuing the drug from a shaky start and for per-
`forming a careful initial study that moves the field
`forward. Whether deferiprone proves to be useful and
`safe will be known in the fullness of time. Whatever
`further studies of the drug reveal, it is comforting to
`know that the search for a better life for patients with
`thalassemia is in reliable hands.
`
`Children’s Hospital
`Boston, MA 02115
`
`D
`
`AVID
`
` G. N
`
`ATHAN
`
`, M.D.
`
`R
`
`EFERENCES
`
`1. Hershko C. Iron chelators in medicine. Mol Aspects Med 1992;13:113-65.
`2. Olivieri NF, Nathan DG, MacMillan JH, et al. Survival in medically treat-
`ed patients with homozygous
`-thalassemia. N Engl J Med 1994;331:574-
`b
`8.
`
`3. Fosburg MT, Nathan DG. Treatment of Cooley’s anemia. Blood 1990;76:
`435-44.
`4. Motekaitis RJ, Martell AE. Stabilities of the iron (III) chelates of 1,2-
`dimethyl-3-hydroxy-4-pyridinone and related ligands. Inorg Chim Acta
`1991;183:71-80.
`5. Lucarelli G, Galimberti M, Polchi P, et al. Bone marrow transplantation in
`patients with thalassemia. N Engl J Med 1990;322:417-21.
`6. Walters MC, Thomas ED. Bone marrow transplantation for thalassemia: the
`USA experience. Am J Pediatr Hematol Oncol 1994;16:11-7.
`7. Vellodi A, Picton S, Downie CJ, Eltumi M, Stevens R, Evans DI. Bone mar-
`row transplantation for thalassaemia: experience of two British centres.
`Bone Marrow Transplant 1994;13:559-62.
`8. Olivieri NF, Brittenham GM, Matsui D, et al. Iron-chelation therapy with
`oral deferiprone in patients with thalassemia major. N Engl J Med 1995;332:
`918-22.
`9. Hider RC, Singh S, Porter JB, Huehns ER. The development of hydroxypy-
`ridin-4-ones as orally active iron chelators. Ann N Y Acad Sci 1990;612:
`327-38.
`10. Porter JB, Hoyes KP, Abeysinghe RD, Brooks PN, Huehns ER, Hider RC.
`Comparison of the subacute toxicity and efficacy of 3-hydroxypyridin-4-one
`iron chelators in overloaded and nonoverloaded mice. Blood 1991;78:2727-
`34.
`11. Wolfe LC, Nicolosi RJ, Renaud MM, et al. A non-human primate model for
`the study of oral iron chelators. Br J Haematol 1989;72:456-61.
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
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`Ex. 2023
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`Vol. 332 No. 14
`
`CLINICAL IMPLICATIONS OF BASIC RESEARCH
`
`955
`
`CLINICAL IMPLICATIONS OF
`BASIC RESEARCH
`
`TELOMERES, CANCER, AND IMMORTALITY
`
` genetic accidents, including the activa-
`N
`UMEROUS
`tion of proto-oncogenes and the loss of tumor-suppres-
`sor genes, can result in the stimulation of cell division.
`However, mammalian cells have evolved an intricate
`set of checks and balances against uncontrolled cellular
`proliferation. One of these is cellular suicide, or apop-
`tosis, triggered by the p53 gene in the presence of ab-
`errant growth signals. Another appears to be the pro-
`gressive shortening of the ends of chromosomes, or
`telomeres, that accompanies normal cell division and
`may contribute to cellular aging. Support for this con-
`cept comes from a recent article in
`by Kim and
`Science
`coworkers,
` reporting a dramatic correlation between
`1
`cancer and the expression of telomerase, an enzyme ca-
`pable of preventing the shortening of telomeres. This
`finding suggests that virtually all cancers must activate
`telomerase in order to overcome a biologic clock, and it
`points to a potentially important new therapeutic tar-
`get in the fight against cancer.
`Telomeres are thought to be critical in maintaining
` In humans they are composed
`chromosomal integrity.
`2
`of a sequence of six nucleotides (thymidine, thymidine,
`adenosine, guanosine, guanosine, and guanosine, or
`TTAGGG) repeated from a few hundred to a thousand
`times. These sequences are synthesized by telomerase,
`a ribonucleoprotein enzyme (composed of both RNA
`and protein). The RNA component contains nucle-
`otides that are complementary to those present in the
`telomere (Fig. 1, inset). By reverse transcription, telo-
`merase makes a DNA copy of its own RNA sequence,
`⬘
`which is then fused to the 3
` terminus of the chromo-
`some. The extension of telomeres by telomerase is re-
`quired to counter the normal shrinkage of chromo-
`somes that occurs after each round of DNA replication.
`Normal replication of a linear DNA strand by DNA
`polymerase is initiated from the site of a bound primer
`⬘
`⬘
`and can proceed only from 5
` to 3
`. Since no primer is
`⬘
`bound at the extreme 5
` end of each chromosome,
`there is a gap in replication, leading to a progressive
`shortening of daughter strands with each round of
`DNA replication. The length of a telomere is thus de-
`termined by the balance between the number of cell di-
`visions and the activity of telomerase.
`The importance of preserving the length of telo-
`meres in continuously dividing cells has been clearly
`demonstrated in yeast and in the protozoan tetrahyme-
`na, in which the inactivation of telomerase results in
`the shrinking of telomeres, chromosomal loss, and
`eventually cell death. In humans, germ cells express tel-
`omerase and maintain their telomere length (along
`with their ability to divide) throughout life. In contrast,
`somatic tissues do not have telomerase activity, and
`they progressively lose telomere length. In a given per-
`son, the telomeres in skin and blood cells are shorter
`than those in germ cells, with an estimated loss of 15 to
`
` Patients with progeria, the
`40 nucleotides per year.
`3,4
`premature aging syndrome, have pronounced shorten-
`ing of telomeres.
` These observations have led to the
`5
`hypothesis that telomere length serves as a biologic
`clock regulating the life span of normal cells (Fig. 1).
`In a manner consistent with this model, cultured nor-
`mal human fibroblasts undergo a finite number of cell
`divisions, after which they enter a state of senescence
`or terminal arrest of growth. The number of cell divi-
`sions correlates well with the initial length of the telo-
`meres, and progressive loss of telomeres is observed in
`culture: 50 to 200 nucleotides are lost with each cell
`doubling, and some 4000 nucleotides are lost by the
`time of senescence.
`5,6
`In contrast to normal cultured cells, tumor-derived
`cell lines that can grow indefinitely in vitro express tel-
`omerase, and their telomeres do not progressively
`shrink. Thus, cancer cells have appropriated a gene
`whose normal function may be to allow germ cells to
`avoid the mortality of somatic cells. The aberrant ex-
`pression of telomerase in cancer cells may result from
`a mutation in the sequences that normally regulate its
`expression, and the timing of that mutation may be in-
`ferred from the length of the telomere itself. Primary
`ovarian tumors expressing telomerase were found to
`have very short telomeres, suggesting that they had un-
`dergone many cell divisions before telomerase was acti-
`vated and telomere length stabilized.
` Thus, the activa-
`7
`tion of telomerase may not be the initial transforming
`event leading to cancer, but rather a late genetic event
`that allows the cancer to progress by conferring immor-
`tality on cancer cells that are already transformed.
`The recent study by Kim et al.
` has demonstrated
`1
`the widespread expression of telomerase in cancer cells,
`implying that telomere stability is critically important
`for the progression of cancer. Since the telomerase gene
`in humans has not been isolated, the authors used a
`sensitive and reliable polymerase-chain-reaction (PCR)
`assay of telomerase enzymatic activity. Ninety of 101
`specimens from primary tumors, representing 12 dif-
`ferent types of cancer, contained telomerase activity,
`whereas none of 50 normal tissues had detectable ac-
`tivity. Similarly, 98 of 100 cancer-derived cell lines
`expressed telomerase, as compared with none of 22
`cultures derived from normal tissues. Benign tumors
`such as leiomyomas and colonic adenomas did not ex-
`press telomerase, and only 1 of 10 specimens of tissue
`affected by benign prostatic hyperplasia showed such
`expression. This striking correlation suggests that the
`expression of telomerase may be a common pathway
`leading to cancer.
`Does this study suggest potential diagnostic or ther-
`apeutic options that would be applicable to a wide
`range of cancers? The extreme sensitivity of the PCR-
`based enzymatic assay allows the detection of 1 cancer
`cell expressing telomerase among 10
` normal cells.
`4
`However, this assay, involving the PCR amplification of
`a synthetic telomere-like DNA target elongated by en-
`dogenous telomerase activity, will need to be adapted
`for general use before its applicability in the diagnosis
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
`Apotex Tech.
`Ex. 2023
`
`

`

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`956
`
`THE NEW ENGLAND JOURNAL OF MEDICINE
`
`April 6, 1995
`
`Normal somatic cells
`
`Normal germ cells or cancer cells
`
`Telomerase
`
`Telomerase
`
`Figure 1. Effect of Telomerase in Normal Germ Cells and Cancer
`Cells.
`In this model the progressive loss of telomeres (red tips of chro-
`mosomes) is associated with the senescence of normal somatic
`cells. The maintenance of normal telomere length is associated
`with the immortality of normal germ cells and cancer cells. The
`inset shows the enzyme telomerase, a ribonucleoprotein with re-
`verse transcriptase activity that catalyzes the extension of telo-
`meric repeats.
`
`Protein
`
`RNA
`
`5ⴕ
`
`Senescence
`
`Immortality
`
`Telomerase
`
`3ⴕ
`
`Telomere
`
`C
`
`A
`
`A U C C
`T T A G G G
`
`tant, this dramatic correlative study must be followed
`by the demonstration that telomerase is the direct
`cause of the immortality of tumor cells. These studies
`await the cloning of the telomerase gene in humans.
`Massachusetts General Hospital
`Boston, MA 02129
`
`of cancer can be tested. Telomerase itself, by virtue of
`its unusual characteristics and absence from somatic
`tissues, could make an excellent target for cancer che-
`motherapy. Its reverse transcriptase activity (analogous
`to that of retroviruses such as the human immunodefi-
`ciency virus) makes it unique among mammalian en-
`zymes and thus offers a potential therapeutic target.
`Similarly, the requirement that telomerase bind to the
`TTAGGG telomere sequence indicates that successful-
`ly blocking this RNA–DNA interaction could inhibit
`the function of the enzyme. An effective inhibitor of tel-
`omerase might induce prompt senescence in rapidly di-
`viding tumors with small telomeres.
`Caution is also warranted, however, before we con-
`clude that a unique cancer marker has been identified.
`In addition to germ cells, hematopoietic and gastroin-
`testinal stem cells could also require telomerase to ful-
`fill their infinite regenerative potential. Most impor-
`
`ANIEL
`
` A. H
`
`ABER
`
`, M.D., P
`
`H
`
`.D.
`
`D
`R
`EFERENCES
`1. Kim NW, Piatyszck MA, Prowse KR, et al. Specific association of human tel-
`omerase activity with immortal cells and cancer. Science 1994;266:2011-5.
`2. Blackburn EH. Structure and function of telomeres. Nature 1991;350:569-73.
`3. de Lange T, Shiue L, Myers RM, et al. Structure and variability of human
`chromosome ends. Mol Cell Biol 1990;10:518-27.
`4. Hastie ND, Dempster M, Dunlop MG, Thompson AM, Green DK, Allshire
`RC. Telomere reduction in human colorectal carcinoma and with ageing. Na-
`ture 1990;346:866-8.
`5. Allsopp RC, Vaziri H, Patterson C, et al. Telomere length predicts replicative
`capacity of human fibroblasts. Proc Natl Acad Sci U S A 1992;89:10114-8.
`6. Harley CB, Futcher AB, Greider CW. Telomeres shorten during ageing of hu-
`man fibroblasts. Nature 1990;345:458-60.
`7. Counter CM, Hirte HW, Bacchetti S, Harley CB. Telomerase activity in hu-
`man ovarian carcinoma. Proc Natl Acad Sci U S A 1994;91:2900-4.
`
`The New England Journal of Medicine
`
`Downloaded from nejm.org by STEFFANY INGS on February 12, 2018. For personal use only. No other uses without permission.
`
` Copyright © 1995 Massachusetts Medical Society. All rights reserved.
`
`Apotex Tech.
`Ex. 2023
`
`