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Molecular Oncology, Markers, Clinical Correlates |
1 The University of Texas M. D. Anderson Cancer Center, Houston, Texas; 2 Dana Farber Cancer Institute, Boston, Massachusetts; 3 Washington University, St. Louis, Missouri; 4 Fox Chase Cancer Center, Philadelphia, Philadelphia; and 5 Massachusetts General Hospital, Boston, Massachusetts
| ABSTRACT |
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Experimental Design: Unstained sections of paraffin-embedded tumor samples were stained with p185/HER2 receptor antibody. Tumors with moderate (2+) to strong (3+) complete membrane staining in at least 10% of the tumor cells were scored as positive for overexpression.
Results: The overall frequency of overexpression for HER2 was 17% (23 of 137), whereas it was only 8% in the three most common histological subtypes screened. Overexpression was distinctly rare in the most common subtype screened, adenoid cystic carcinoma (4%, 3 of 70). Overexpression was very common in salivary duct cancers; 10 (83%) of 12 were positive for HER2. This observation is consistent with the typical high-grade histological features and aggressive behavior of this subtype as well as with its histogenetic similarity to breast cancer. Analysis based on histogenesis (intercalated duct versus excretory duct) indicated a higher frequency of overexpression in the latter (55%) than in the former (7%).
Conclusions: Our overall results suggest that trastuzumab will not have a major role in treatment of salivary gland cancers of intercalated duct origin. Further systematic evaluation of trastuzumab in subtypes of excretory duct origin could be supported.
| INTRODUCTION |
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0.9 of 100,000 with 2,500 new cases annually in the United States. The majority of these arise in the parotid (70%) and, of these,
25% are malignant. The incidence of malignancy at other sites, such as submandibular, sublingual, or minor salivary glands, is higher, approximating 50% (1)
. Histopathologically they are composed of widely varied morphological subtypes with heterogeneous clinical behavior. In general, cancers of intercalated duct origin (adenoid cystic, adenocarcinoma, acinic cell, polymorphous low-grade adenocarcinoma, and myoepithelial) are low grade and biologically indolent compared with those derived from the secretory duct (salivary duct, mucoepidermoid, and squamous; Refs. 2 , 3 ).
Salivary gland malignancies are managed primarily with surgical resection and, if indicated by postoperative pathological findings of stage or grade, or perineural invasion, adjunctive radiation. Systemic therapy is generally reserved for locoregional recurrence and/or metastatic disease, the risk of which is correlated with advanced stage, higher grade, and certain histological subtypes (1) . Although cytotoxins such as doxorubicin, cisplatin, 5-fluorouracil, paclitaxel, and navelbine clearly have some degree of activity in this disease, response rates are generally in the range of 1530%, and responses are relatively short in duration (4, 5, 6, 7, 8) . Given the rarity of these tumors and the variability in natural history of metastatic disease, with prolonged indolent courses in many patients, it has been difficult to define the survival benefits of cytotoxic agents. Therefore, there is a need to better understand the biology of these cancers and to develop therapeutic approaches based on relevant targets.
In that context, we evaluated expression of HER2 in recurrent salivary gland carcinomas as part of a clinical trial to define the clinical activity of trastuzumab, a recombinant monoclonal antibody directed against HER2, in these tumors. The HER2 proto-oncogene on chromosome 17q is expressed or overexpressed in a variety of epithelial malignancies (9) . The gene encodes a membrane receptor protein that is one of four members of the epidermal growth factor receptor family. HER2 has no known ligand but is capable of heterodimerization with any of the other three HER proteins, and can, thus, participate in effecting a signal transduction cascade with diverse effects that potentiate the malignant phenotype (10) . In breast cancer, overexpression of HER2 is correlated with gene amplification, conferring a poor prognosis and relative resistance to cytotoxics (11 , 12) . Trastuzumab is active as a single agent and enhances the rate of response to cytotoxics in HER2-positive breast cancers (13) .
In previous reports, frequency of HER2 expression in salivary gland carcinomas, which was detected by either immunostaining or fluorescence in situ hybridization, has been variable. Rates of 7 and 56% in adenoid cystic (14, 15, 16) , 3038% in mucoepidermoid (14 , 17) , and 23% in terminal duct adenocarcinoma (14) subtypes have been documented. In two reports, overexpression and/or amplification of HER2 was an independent marker of poor prognosis in mucoepidermoid and adenoid cystic carcinomas (14 , 17) . These data and the availability of trastuzumab provided the rationale for our prospective evaluation of HER2 expression in patients with incurable salivary gland cancer.
Patients with tumors that overexpressed the protein were evaluated for participation in a Phase II clinical trial with trastuzumab, the complete results of which are reported separately (18) . Patients were accrued into two strata on the basis of presumed tumor origin from the intercalated or excretory duct.
| MATERIALS AND METHODS |
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Assessment of HER2 Expression.
Slides were scored on a 03+ scale, as follows: 0, staining in <10% of tumor cells or no staining; 1+, faint and partial membrane staining in
10% of tumor cells; 2+, weak to moderate complete membrane staining in
10% of tumor cells; or 3+, moderate to strong complete membrane staining in
10% of tumor cells. Scores of either 2+ or 3+ were defined as overexpression. Two independent observers scored the slides, and discrepancies were resolved by consensus.
| RESULTS |
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6% of the specimens analyzed. In addition to the tumors listed in Table 2
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Analysis based on origin indicates that 55% (16 of 31) of excretory duct origin tumors were HER2 positive, whereas only 7% (7 of 105) of tumors thought to originate from the intercalated duct were HER2 positive.
The results of weekly trastuzumab therapy in 14 patients from the screened population are reported by Haddad et al. (18) . To summarize, one of three patients with mucoepidermoid cancer had a partial response that is ongoing at 45 months. Two additional patients with salivary duct cancer had stable disease for 24 and 40 weeks. These two patients are grouped with adenocarcinoma by Haddad et al. (18) . Although no other patients had response or stable disease beyond 12 weeks, the numbers of patients within each subtype are too small to exclude trastuzumab as an active agent.
| DISCUSSION |
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The clinical trial with trastuzumab was originally designed to accrue patients in two strata based on tumor origin: group 1 (intercalated duct) including adenoid cystic, acinic cell, adenocarcinoma, malignant mixed, and myoepithelial subtypes; and group 2 (excretory duct), including mucoepidermoid, squamous, and salivary duct subtypes. In the first stage of a Simon two-stage design, response assessment in 15 patients of each stratum was planned, and 1 response of 15 would support accrual to a total of 25 patients in that group. The low frequency of HER2 positivity in the screened population, especially in the most common adenoid cystic subtype, led to an impression of low feasibility and closure of the trial when only 14 patients total had been accrued (7 in each group). The one patient with partial response and the two with prolonged stability all had tumor origin from the excretory duct.
In retrospect, the pattern of HER2 positivity suggests a higher frequency in malignancies of excretory duct origin than in those of intercalated duct origin: 55% (16 of 31) versus 7% (7 of 106). In fact, the one response to trastuzumab was in a tumor of excretory duct origin. This response is quite intriguing because of its long duration. An argument to further evaluate trastuzumab in this particular group can be made on the basis of the original statistical design of the trial and the screening data. Because of the rarity of recurrent salivary gland cancer, and especially tumors of excretory duct origin, which represented only 22% of the screened cases, a trial such as this will have low feasibility without collaboration among multiple large tertiary centers or through the intergroup mechanism.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Notes: A. D. C. is currently at National Cancer Institute, NIH, Bethesda, Maryland.
Requests for reprints: Bonnie Glisson, The University of Texas M. D. Anderson Cancer Center, Department of Thoracic/Head & Neck, Box 432, 1515 Holcombe Boulevard, Houston, TX 77030. Phone: (713) 792-6363; Fax: (713) 796-8655; E-mail: bglisson{at}mdanderson.org
Received 9/17/03; revised 10/ 7/03; accepted 10/14/03.
| REFERENCES |
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