Novel Immunologic and Biologic
`Therapies for Breast Cancer
`John C. Gutheil, MD
`
`Address
`Clinical Research and Development, Vical, Inc.,
`9373 Towne Centre Drive, Suite 100, San Diego, CA 92121, USA.
`E-mail: Jgutheil@vical.com
`Current Oncology Reports 2000, 2:582–586
`Current Science Inc. ISSN 1523–3790
`Copyright © 2000 by Current Science Inc.
`
`The treatment of breast cancer has benefited substantially
`from the introduction of trastuzumab in 1998. Yet
`trastuzumab only represents the first of a series of newer
`biologic therapies that will change the manner in which
`patients with breast cancer are treated. Initially, biologic
`therapies will be used in combination with existing chemo-
`therapeutic agents. However, as biologic therapies improve,
`chemotherapeutic agents are likely to be replaced with
`biologic agents that are more effective, less toxic, and more
`patient- and tumor-specific. Promising classes of agents
`include monoclonal antibodies and cancer vaccines.
`
`Introduction
`The US Food and Drug Administration (FDA) approval of
`trastuzumab in September 1998 signaled a fundamental
`change in the way that oncologists approach patients with
`breast cancer. Although chemotherapy remains the pre-
`dominant systemic therapy, treatments aimed at recruiting the
`immune system into the battle against cancer increasingly
`command the attention of scientists, physicians, and the
`public. Breast cancer is evolving into a disease in which
`traditional therapies such as surgery, radiation, and chemo-
`therapy will be followed by or used in conjunction with
`biologic therapies that augment the immune response of
`patients to their own tumor. With further development, bio-
`logically directed or immune-based therapies may supplant
`traditional therapies as front-line treatment for breast cancer.
`Consequently, physicians will need a solid understanding of
`the role of the immune system in controlling cancer, and they
`will be asked to choose among an increasing number of novel
`therapies available to patients with breast cancer.
`
`Antibody Therapy for Breast Cancer
`Early studies made use of polyclonal, non-human antibodies
`harvested from the sera of animals immunized with the
`antigen of interest. As such, limited antibody availability,
`
`poorly defined antigenic targets, and rapid clearance of non-
`human antibodies from the circulation hampered the
`development of effective therapies. Issues surrounding
`antibody availability and poorly defined antigenic targets
`were solved with the discovery of monoclonal antibodies in
`1975 by Kohler and Milstein [1]. These early monoclonal
`antibodies allowed for an endless supply of well-character-
`ized antibodies. However, they were generated in non-
`human systems, and were thus viewed by the patient’s
`immune system as a foreign, non-human protein.
`Consequently, patients often developed humoral immune
`responses (ie, antibodies) against the foreign immuno-
`globulin. The use of non-human monoclonal antibodies in
`humans is therefore generally limited to short-term or single-
`dose administration [2].
`The development of chimeric or humanized mono-
`clonal antibodies allowed patients to be treated repeatedly
`with the same monoclonal agent for extended periods of
`time [3]. With such antibodies, the likelihood of develop-
`ing an immune response to repeated administration in
`humans is extremely low [4••]. Indeed, today, the major
`remaining obstacle to developing additional effective anti-
`bodies for the treatment of cancer is identification of
`appropriate antigen targets.
`The bioengineering of therapeutic antibodies is not
`limited to the humanization of non-human monoclonal
`antibodies [5]. The same techniques that have been used to
`develop less immunogenic monoclonal antibodies have
`also been used to alter the basic structure of antibodies.
`Examples include antibody fragments, bispecific
`antibodies, and antibody conjugates with toxins, chemo-
`therapeutic agents, or radiopharmaceuticals. Each of these
`antibody constructs retains most or all of the native ability
`of the antibody to bind to specific antigens with high
`affinity, and in addition has altered pharmacologic or
`immune properties better suited for a defined task.
`Examples of several are discussed in the following sections.
`
`Trastuzumab
`Trastuzumab was engineered from a mouse monoclonal
`antibody (4D5) directed against the HER2 transmembrane
`protein. Trastuzumab differs from the parent mouse
`monoclonal in that the majority of non-antigen binding
`sequences have been replaced with human sequences. The
`HER2 protein was chosen as a target for therapy based on
`its overexpression in approximately 25% of women with
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`breast cancer and its correlation with poor outcome in
`these patients [4••].
`Trastuzumab received FDA approval for use in the
`United States in 1998 based on the results of two large
`trials. The first evaluated use of trastuzumab was as a
`single agent in 222 patients with recurrent or refractory
`metastatic breast cancer. This phase II trial demonstrated a
`15% response rate (partial response [PR] + complete
`response [CR]) and a 9-month median duration of
`response. As expected, the incidence of human anti-mouse
`antibodies (HAMA) following use of this humanized
`monoclonal antibody was low, with only one of 211
`patients (0.5%) demonstrating antibodies against trastu-
`zumab. Unexpectedly, there was a high incidence of
`cardiac dysfunction, with 10 patents (4.7%) experiencing
`clinical congestive heart failure, cardiomyopathy, or a
`decrease in ejection fraction of greater than 10% [4••].
`The second trial evaluated the use of trastuzumab in
`combination with chemotherapy in the setting of first-line
`metastatic disease. Patients with prior exposure to anthra-
`cyclines received paclitaxel at 175 mg/m2 every 3 weeks.
`Patients without prior anthracycline exposure received doxo-
`rubicin (60 mg/m2) and cyclophosphamide (600 mg/m2)
`every 3 weeks. In addition, patients were randomized to
`either no additional therapy or combination therapy with
`trastuzumab (4 mg/kg loading followed by 2 mg/kg/wk). In
`the preliminary report of the study, the response rate to
`chemotherapy was significantly improved with the addition
`of trastuzumab [6]. This effect was most pronounced for
`those patients treated with paclitaxel, in whom the response
`rate increased from 15% with paclitaxel alone to 38% with
`paclitaxel and trastuzumab. Responses in patients receiving
`trastuzumab were also more durable. The median duration
`of response increased from 4 months in the group receiving
`paclitaxel alone to 8 months for the group receiving
`paclitaxel with trastuzumab [6].
`Many questions remain concerning the optimal dose,
`schedule, and setting in which to use trastuzumab. The
`currently approved dose and schedule for trastuzumab was
`chosen based on the assumption that plasma levels of
`trastuzumab needed to mimic levels known to be active in
`vitro (10 ␮g/mL) [4••]. Consequently, plasma trough
`levels generally exceed 10 ␮g/mL shortly after the initiation
`of weekly therapy at 2 mg/kg. Nonetheless, it is possible
`that doses and schedules exist other than those currently
`approved by the FDA that are more effective or more
`convenient for the patient.
`The use of trastuzumab in combination with paclitaxel
`was not part of the initial trial design testing trastuzumab
`in combination with chemotherapy. It was only after
`difficulty arose in accruing patients to a study employing
`doxorubicin and cyclophosphamide as therapy for first-
`line metastatic disease that a provision for treatment of
`patients with prior anthracycline was added (Shak S, Per-
`sonal communication). It is therefore intriguing to ask
`what other chemotherapeutic agents might show signifi-
`
`cantly increased efficacy when administered with trastu-
`zumab. Along those lines, Pegram et al. [7] evaluated
`trastuzumab in combination with cisplatin in a phase II
`study and demonstrated an overall response rate of 24%.
`In the preclinical setting, trastuzumab appears to augment
`the activity of most anticancer drugs (Slamon D, Personal
`communication). Selection of the best combination is
`complicated by the fact that many of these drugs are not
`considered optimal therapy for patients with metastatic
`breast cancer.
`Trastuzumab cardiotoxicity remains an unfortunate
`and poorly explained attribute of this antibody. Preclinical
`data did not suggest that this toxicity would be seen in
`humans, and in fact, serial cardiac evaluations were only
`included in the initial registration trial as the standard of
`care for those patients receiving anthracycline. Although a
`number of theories have been suggested about the cause
`of trastuzumab cardiotoxicity, no single theory currently
`explains this troublesome phenomenon, and no effective
`means to abrogate this toxicity has been found [8••].
`Perhaps the greatest challenge will be to define the
`role of trastuzumab in the adjuvant setting. Currently, a
`number of clinical trials are either planned or in progress
`for this indication. Of particular concern is the issue of
`combining trastuzumab with anthracycline. Although no
`trial in the adjuvant setting is evaluating the use of
`trastuzumab and anthracycline simultaneously, whether
`administration of these two agents sequentially will result
`in an acceptably safe regimen remains to be seen. Other
`investigators have chosen to evaluate non-anthracycline–
`based chemotherapy in combination with trastuzumab in
`the hope that the addition of trastuzumab will more than
`offset the absence of anthracycline. In either case, concern
`has been raised that long-term side effects may result
`from use of trastuzumab—particularly delayed or acceler-
`ated cardiac dysfunction that was not apparent from the
`initial registration trials.
`
`Edrecolomab
`Edrecolomab is a murine monoclonal antibody (17-1A)
`directed against the epithelial adhesion molecule EpCAM.
`EpCAM is widely expressed in epithelial tumors, which led
`to its evaluation in the adjuvant setting of colorectal
`cancer. Edrecolomab received approval for this indication
`in Germany in December 1994. This antibody may gain
`approval in the United States pending the results of a US
`trial conducted for the same indication. As with HER2,
`which is expressed in many different tumors of epithelial
`origin, 17-1A is found in both colon and breast tumors.
`For this reason, Braun et al. [9••] evaluated the ability of
`this antibody to clear the bone marrow of microscopic
`residual disease in patients with metastatic breast cancer.
`They report that a single dose of edrecolomab (500 mg,
`intravenously) resulted in a one-log reduction in
`detectable tumor cells in the marrow of 10 patients with
`breast cancer.
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`Microscopic residual disease in the marrow may be a
`more appropriate target for adjuvant therapies, and the
`ability to clear such microscopic disease may serve as a
`surrogate marker for the effectiveness of adjuvant therapies
`in the future [10]. Use of such a surrogate could speed the
`development of adjuvant therapies, which currently
`depend on the completion of large clinical trials requiring
`long follow-up [11•]. The investigators also point out that
`tumor cells are far from uniform in their expression of sur-
`face antigens, and for this reason, it is likely that future
`therapies will include cocktails of antibodies or will consist
`of therapies that are capable of attacking poly-antigen
`targets (ie, vaccination).
`
`Bispecific antibody (MDX-H210)
`with granulocyte-colony stimulating factor
`Native antibodies have two antigen-binding sites per
`molecule, both of which share the same binding specificity
`and affinity. However, it is possible to bioengineer anti-
`bodies with two different binding sites per molecule. The
`result is a “bispecific” antibody with the ability to cross-
`link structures containing the two antigens of interest.
`Pullarkat et al. [12] evaluated the utility of a bispecific anti-
`body (MDX-H210) with affinity for both HER2 and the
`FcGamma receptor (CD64) in patients with breast cancer.
`The ability of MDX-H210 to bind to both HER2 and CD64
`was anticipated to result in coupling of immune effector
`cells, specifically T cells, to breast cancer cells expressing
`HER2. Such coupling was expected to lead to immune
`activation and destruction of HER2 positive tumor cells. As
`with many biologic therapies, no maximum tolerated dose
`was reached in this phase I/II trial. Changes were observed
`in the immune parameters of patients (expression of IL-6,
`G-CSF, and TNF-a
` and recruitment of monocytes into the
`periphery), consistent with the purported mechanism of
`action of this compound, but no tumor responses were
`seen. Rather, dose escalation was halted at the highest
`available dose (40 mg/m2) in the absence of significant
`toxicity. Whereas the lack of tumor responses in this
`patient population was disappointing, the ability to
`control the trafficking of specific immune cells should
`prove useful in designing therapies in the future.
`
`bearing tissue. Wong et al. [13] evaluated an Yttrium-90–
`labeled antibody (T84.66) in seven patients with refractory
`breast cancer. T84.66 is a human/mouse chimeric antibody
`with specificity for carcinoembryonic antigen (CEA). Given
`the expectation that dose-limiting toxicity would be hema-
`tologic, patients received stem-cell support in order to
`allow further dose escalation. Evidence of an antitumor
`response was seen in two of seven patients, but no patient
`demonstrated a complete or partial response.
`Antibodies can also be coupled to cytotoxic molecules
`in an attempt to increase the therapeutic index of the
`native cytotoxic. BMS-182248-1 is such a molecule and
`consists of doxorubicin linked to an antibody directed
`against the Lewis-Y antigen. Lewis-Y is expressed by many
`epithelial tumors, including the majority of breast cancers.
`Tolcher et al. [14] compared this antibody conjugate with
`standard doxorubicin in 23 women in a randomized phase
`II study. Unfortunately, responses were seen in only one of
`14 patients receiving BMS-182248-1 and four of nine
`patients receiving standard doxorubicin. In addition, gas-
`trointestinal toxicity in the group receiving BMS-182248-1
`included significant gastritis, nausea, and vomiting and
`elevations in both amylase and lipase. The authors
`concluded that the profound gastric toxicity was likely
`related to binding of BMS-182248-1 to normal tissues
`expressing the Lewis-Y antigen. Further development of
`BMS-182248-1 was not recommended.
`It bears repeating that the toxicity of any immuno-
`conjugate or antibody is not always predictable. Trastu-
`zumab demonstrated unexplained cardiotoxicity when it
`was first used in humans, and BMS-182248-1 demon-
`strated profound gastrointestinal toxicity, which was not
`commonly seen with either doxorubicin or the native anti-
`body alone. Another example of unexpected toxicity comes
`from the experience of Pai-Scherf et al. [15], who evaluated
`a single-chain immunotoxin consisting of the antigen-
`binding portion of an anti-erbB2 antibody bound to a
`truncated portion of Pseudomonas exotoxin A. In their
`study, five patients with breast cancer treated with this
`immunotoxin developed hepatotoxicity believed to be due
`to the presence of erbB-2 on normal hepatocytes.
`
`Immuno-conjugates
`Another permutation on the theme of using antibodies to
`treat cancer involves the development of antibody con-
`jugates. Interestingly, with careful selection of the coupling
`site, most antibodies will tolerate linkage to large mole-
`cules with only minor changes in their binding affinity to
`antigen. Coupling a compound to an antibody was thus
`recognized early on as an ideal strategy for focusing the
`effect of a cytotoxic agent or radioisotope to areas of
`antigen distribution.
`Coupling radioactive isotopes to antibodies offers the
`advantage of delivering high doses of radiation to areas of
`antigen concentration while sparing normal, non-antigen–
`
`Use of Antibodies in the Future
`Antibodies continue to offer the promise of less toxic
`therapy for patients with cancer. However, much work
`remains to be done. As new antibodies are introduced,
`each will require further evaluation to determine its
`optimal dose, schedule, and appropriate clinical setting.
`Initially, antibodies will be used in conjunction with
`currently accepted therapy such as radiation and chemo-
`therapy. As more is learned about the immune system and
`cancer, and as we become better able to recruit the immune
`system to fight cancer, we will see immune therapies
`augment and possibly supplant chemotherapy and radio-
`therapy as the preferred method of treatment.
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`Vaccine Therapy
`Vaccination has theoretic advantages over passive (antibody
`administration) immunization for the treatment of cancer.
`Although one could conceivably administer a cocktail of
`antibodies that would cover many different antigens
`present on a tumor cell, current antibody therapies (such as
`trastuzumab) are directed against specific monoclonal
`targets (such as HER2). Cancer cells lacking these targets or
`cells capable of reducing or eliminating these targets on
`their surface are therefore capable of surviving in the face of
`such monospecific antibody therapy.
`Active immunization (ie, following successful vaccina-
`tion) results in a more robust immune response than is
`possible following antibody administration. Generally, an
`antibody response following immunization is not limited
`to a single monospecific antibody. Rather, a polyclonal
`response is elicited, resulting in generation of antibodies
`that may cover a wide range of cellular targets. Active immu-
`nization may also generate a cellular immune response in
`addition to a humoral or antibody response. Such cellular
`responses can be important in eliciting an immune reaction
`against intracellular targets.
`Simple administration of tumor antigens to a patient is
`unlikely to elicit a meaningful immune response. Rather,
`most vaccination strategies include the use of an adjuvant
`in the vaccine preparation such as granulocyte-macrophage
`stimulating factor (GM-CSF) or keyhole-limpet hemo-
`cyanin (KLH). Several vaccines also make use of a priming
`dose of cyclophosphamide, which has been demonstrated
`to increase antibody titers following vaccination in
`humans. Other strategies include alteration of the native
`antigen in the hope that slight changes in the tertiary
`structure or sequence will render the vaccine more likely to
`be viewed as foreign by the immune system. Interestingly,
`small peptides derived from larger proteins are often
`capable of eliciting an immune response where the intact
`protein is not. This is presumably due to the differences in
`folding and orientation between a native protein and a
`small fragment of that protein presented to the immune
`system “out of context.” Such “peptide” vaccines are a
`promising approach to cancer vaccination.
`Sandmaier et al. [16] reported on the use of such a
`vaccine against carbohydrate antigens in patients following
`cytoreduction with a stem-cell transplant. Concern has
`been raised about the ability of such patients to mount a
`meaningful immune response following transplantation.
`These authors demonstrate that the majority of such
`patients can mount an immune response to the specific
`carbohydrate used in the vaccine, sialyl-Tn. Seventeen of 27
`patients receiving at least three vaccinations demonstrated
`evidence of a T cell–based response that was specific for
`sialyl-Tn. Furthermore, in those patients with elevated
`tumor markers at the time of vaccination, five of seven
`demonstrated decreasing markers over time. This promis-
`ing vaccination strategy is currently being evaluated in a
`
`phase III trial in patients with metastatic breast cancer
`following cytoreductive chemotherapy.
`Disis et al. [17••] evaluated a peptide-based vaccine
`using GM-CSF as an adjuvant treatment in patients with
`breast and ovarian cancer. Peptide segments were chosen
`from the larger HER2 protein using a computer program
`that selected peptide fragments likely to elicit a cellular
`immune response. Peptide sequences were chosen from
`both the intracellular and extracellular domain of the
`HER2 protein in anticipation that intracellular peptides
`might be more likely to be immunogenic. All patients
`developed T-cell responses to the peptides administered in
`the vaccine, and most patients also developed reactions
`against other peptides in HER2 that were not included in
`their vaccine. The induction of an immune response to
`portions of a protein not included in a vaccine is referred
`to as epitope spreading and is considered to be important
`when eliciting a cellular immune response to a tumor.
`Tumor cells have more difficulty escaping an immune
`reaction directed at multiple targets in the cell as opposed
`to an immune reaction focused on a single epitope or
`antigen. Interestingly, the extracellular sequences were as
`good at eliciting an immune response as were the intra-
`cellular sequences.
`Vaccines require time to be effective and for that reason
`are unlikely to benefit patients with advanced cancer. Con-
`sequently, most vaccine strategies represent an attempt to
`treat patients in a situation of minimal residual disease
`such as that seen following successful treatment with
`chemotherapy, radiotherapy, or surgery. Given the myriad
`of tumor types and the uncertainty of developing tumors
`even in high-risk individuals, it is unlikely that cancer
`vaccines will be used in patients who are only “at risk” for
`tumor development.
`
`Conclusions
`Cancer therapy has progressed dramatically in the past
`decade and will continue to improve in the future. Cancer
`therapies will be less toxic, more patient specific, and
`almost certainly designed to recruit the patients’ immune
`system into the battle against their tumor. The development
`of these new therapies will require a change in the manner
`in which we conduct clinical trials. We will no longer be
`able to make use of a drug’s toxicity to guide its dosing;
`rather, we will be required to develop new endpoints such
`as the clearance of tumor cells from bone marrow, or the
`resolution of specific genetic markers from the blood.
`Similarly, response rates may be less important in decisions
`regarding whether a drug warrants further development.
`The development of new biologic therapies will be
`greatly facilitated in those situations where the mechanism
`of action is clearly defined (as was the case with trastu-
`zumab). Such an understanding allows for the targeting of
`patient populations with the highest likelihood of benefit.
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`In addition, new biologic therapies are likely to be used and
`developed in combination with existing therapies, parti-
`cularly chemotherapy. Given the favorable toxicity profiles
`of newer biologic therapies, such combinations will be
`practical. The identification of effective combinations will
`provide insight into the mechanism of action of both the
`biologic therapy and existing chemotherapy. As with most
`drugs currently in clinical practice, the optimal combina-
`tions and schedules will be determined empirically in the
`setting of clinical trials performed long after drug approval
`by the FDA.
`
`References and Recommended Reading
`Papers of particular interest, published recently, have been
`highlighted as:
`• Of importance
`•• Of major importance
`
`2.
`
`3.
`
`1. Kohler G, Milstein C: Continuous cultures of fused cells
`secreting antibody of predefined specificity. Nature 1975,
`256:495–497.
`Tjandra JJ, Ramadi L, McKenzie IF: Development of human
`anti-murine antibody (HAMA) response in patients. Immunol
`Cell Biol 1990, 68 (Pt 6):367–376.
`Takeda S, Naito T, Hama K, et al.: Construction of chimaeric
`processed immunoglobulin genes containing mouse variable
`and human constant region sequences. Nature 1985,
`314:452–454.
`4.•• Cobleigh MA, Vogel CL, Tripathy D, et al.: Multinational study
`of the efficacy and safety of humanized anti-HER2 mono-
`clonal antibody in women who have HER2-overexpressing
`metastatic breast cancer that has progressed after chemo-
`therapy for metastatic disease. J Clin Oncol 1999,
`17:2639–2648.
`One of two studies used to support approval of trastuzumab in the
`United States.
`Buchsbaum DJL: Experimental approaches to increase radio-
`5.
`labeled antibody localization in tumors. Cancer Res 1995,
`55(suppl 23):5729s–5732s.
`Slamon DJ, Leyland-Jones B, Shak S: Addition of Herceptin
`(humanized anti-HER2 antibody) to first line chemotherapy
`for HER2 overexpressing metastatic breast cancer refractory
`to chemotherapy treatment [abstract]. Proc ASCO 1998,
`17:98a.
`Pegram MD, Lipton A, Hayes DF, et al.: Phase II study of
`receptor-enhanced chemosensitivity using recombinant
`humanized anti-p185HER2/neu monoclonal antibody plus
`cisplatin in patients with HER2/neu-overexpressing
`metastatic breast cancer refractory to chemotherapy
`treatment. J Clin Oncol 1998, 16:2659–2671.
`
`6.
`
`7.
`
`8.•• Ewer MS, Gibbs HR, Swafford J, Benjamin RS: Cardiotoxicity in
`patients receiving trastuzumab (Herceptin): primary toxicity,
`synergistic or sequential stress, or surveillance artifact?
`Semin Oncol 1999, 26(suppl 12):96–101.
`An excellent review of the issues surrounding trastuzumab cardiotoxicity.
`9.•• Braun S, Hepp F, Kentenich CR, et al.: Monoclonal anti-
`body therapy with edrecolomab in breast cancer patients:
`monitoring of elimination of disseminated cytokeratin-
`positive tumor cells in bone marrow. Clin Cancer Res 1999,
`5:3999–4004.
`An interesting use of edrecolomab as treatment for microscopic
`residual disease in the bone marrow is reported. This may represent a
`new method of evaluating adjuvant therapies in the future.
`Braun S, Pantel K, Muller P, et al.: Cytokeratin-positive cells in
`10.
`the bone marrow and survival of patients with stage I, II, or
`III breast cancer. N Engl J Med 2000, 342:525–533.
`11.• Braun S, Kentenich C, Janni W, et al.: Lack of effect of adjuvant
`chemotherapy on the elimination of single dormant tumor
`cells in bone marrow of high-risk breast cancer patients.
`J Clin Oncol 2000, 18:80–86.
`The authors present a possible explanation for the inability of chemo-
`therapy to clear microscopic residual disease from the majority of
`patients undergoing adjuvant therapy.
`Pullarkat V, Deo Y, Link J, et al.: A phase I study of a HER2/neu
`12.
`bispecific antibody with granulocyte-colony-stimulating
`factor in patients with metastatic breast cancer that over-
`expresses HER2/neu. Cancer Immunol Immunother 1999,
`48:9–21.
`13. Wong JY, Somlo G, Odom-Maryon T, et al.: Initial clinical
`experience evaluating Yttrium-90-chimeric T84.66 anti-
`carcinoembryonic antigen antibody and autologous
`hematopoietic stem cell support in patients with carcino-
`embryonic antigen-producing metastatic breast cancer.
`Clin Cancer Res 1999, 5(suppl 10):3224s–3231s.
`Tolcher AW, Sugarman S, Gelmon KA, et al.: Randomized
`phase II study of BR96-doxorubicin conjugate in patients
`with metastatic breast cancer. J Clin Oncol 1999, 17:478–484.
`Pai-Scherf LH, Villa J, Pearson D, et al.: Hepatotoxicity in can-
`cer patients receiving erb-38, a recombinant immunotoxin
`that targets the erbB2 receptor. Clin Cancer Res 1999, 5:2311–
`2315.
`Sandmaier BM, Oparin DV, Holmberg LA, et al.: Evidence of a
`cellular immune response against sialyl-Tn in breast and
`ovarian cancer patients after high-dose chemotherapy, stem
`cell rescue, and immunization with Theratope STn-KLH
`cancer vaccine. J Immunother 1999, 22:54–66.
`17.•• Disis ML, Grabstein KH, Sleath PR, Cheever MA: Generation
`of immunity to the HER-2/neu oncogenic protein in patients
`with breast and ovarian cancer using a peptide-based
`vaccine. Clin Cancer Res 1999, 5:1289–1297.
`A good example of peptide-based vaccines is presented, along with a
`helpful discussion of the issues surrounding vaccine development.
`
`14.
`
`15.
`
`16.
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