Invasive Micropapillary Carcinoma with CEP17 Monosomy of the Bilateral Breast: A Rare Case Report and Review of the Literature.

Invasive micropapillary carcinoma (IMPC) is a novel type of breast cancer which is potentially very aggressive and may show early lymphatic infiltration. Monosomy of chromosome 17 (m17) is rare in breast cancer, and according to the 2018 guidelines of the American Society of Clinical Oncology/College of American Pathologists, the decision to administer trastuzumab treatment should be made based on positive human epidermal growth factor receptor 2 results by immunohistochemistry. Here, we report a rare case of bilateral local advanced IMPC involving m17. A 33-year-old woman found a mass measuring 30 mm on the left breast that increased to 100 mm over 3 months. A diagnosis of IMPC was made based on the findings of core needle biopsies of bilateral breast masses and left axillary lymph node, and m17 was detected by fluorescence in situ hybridization (FISH). The patient underwent 6 cycles of neoadjuvant chemotherapy (docetaxel, epirubicin, and cyclophosphamide) and left-side modified radical mastectomy, left axillary lymph node dissection, right breast-conserving surgery, and right sentinel lymph node biopsy. Postoperative pathologic analysis of both breasts revealed IMPC, and m17 was confirmed by FISH. The patient received radiotherapy and endocrine therapy but rejected trastuzumab treatment. The patient was still alive at the 30-month follow-up, without recurrence or metastasis. Our findings suggest that loss of chromosome 17 may influence prognosis or therapeutic response, which needs to be further confirmed.