Abstract
Human epidermal growth factor receptor 2 (HER2) positive (+) classical type invasive lobular carcinoma (cILC) of the breast is extremely rare and its clinicopathologic features have not been well characterized. We compared features of HER2(+) and HER2 negative (−) cILCs. A total of 29 cases were identified from the clinical database at our institution from 2011-2019; 9 were HER2(+) cILC tumors and 20 were HER2(−) cILC tumors. The results reveal that HER2(+) cILC group had significantly increased Ki-67 expression and reduced estrogen receptor (ER) expression compared to HER2(−) cILC group (both p < 0.05). In addition, HER2(+) cILCs tended to be diagnosed at a younger age and more common in the left breast, and appeared to have a higher frequency of nodal or distant metastases. These clinicopathologic features suggest HER2(+) cILC tumors may have more aggressive behavior than their HER2(−) counterpart although both groups of tumors showed similar morphologic features. Future directions of the study: (1) To conduct a multi-institutional study with a larger case series of HER2(+) cILC to further characterize its clinicopathologic features; (2) to compare molecular profiles by next generation sequencing (NGS) assay between HER2(+) cILC and HER2(−) cILC cases to better understand tumor biology of this rare subset of HER2(+) breast cancer; and (3) to compare molecular characteristics of HER2(+) cILC and HER2(+) high grade breast cancer in conjunction with status of tumor response to anti-HER2 therapy to provide insight to management of this special type of low grade breast cancer to avoid unnecessary treatment and related toxicity
Highlights
Invasive lobular carcinoma (ILC) accounts for 3–15% of all invasive breast carcinomas [1,2,3,4,5,6,7,8]
Tumors and 11 of 20 (55.0%) Human epidermal growth factor receptor 2 (HER2)(−) classical type of ILC (cILC) were on the left breast (p = 0.076, chi-square test)
One patient with HER2(−) cILC was excluded from evaluation of status of nodal and distant metastasis because she did not receive surgery and/or systemic therapy due to her age (93 years-old) and other disease
Summary
Invasive lobular carcinoma (ILC) accounts for 3–15% of all invasive breast carcinomas [1,2,3,4,5,6,7,8]. Newman published the first large case series of lobular carcinoma in which he identified 142 of 1396 (10.1%) breast cancer cases to be terminal duct/lobular type [6]. Among these 142 tumors, he found 73 tumors are “pure” lobular type (51.4%), i.e., classical type based on the exclusive “single cell” pattern
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