A case of invasive lobular carcinoma with signet-ring-cell differentiation treated with multidisciplinary therapy: a rare case report.

BACKGROUND: Invasive lobular carcinoma (ILC) with signet-ring-cell (SRC) differentiation of the breast is a relatively rare disease and is reported to frequently metastasize to the gastrointestinal and urinary systems. CASE PRESENTATION: A 66-year-old woman presented for routine breast cancer screening without any subjective symptoms. A mass detected in the upper-outer region of her right breast. Core needle biopsy led to the diagnosis of ILC with SRC of the breast. Positron emission tomography-computed tomography, urine cytology, and upper and lower gastrointestinal endoscopy revealed no abnormal findings, and the disease was diagnosed as cT1cN0M0, Stage I. Immunohistochemical examination showed estrogen receptor (ER)-positive (10%, weak), progesterone receptor (PgR)-negative (0%), human-epidermal growth factor receptor 2 (HER2) score 0, and Ki-67 index of 9.8%, suggesting a luminal B-like subtype. The patient received 4 cycles of epirubicine and cyclophosphamide followed by 4 cycles of docetaxel (DTX) as neoadjuvant chemotherapy (NAC). Because prolonged neutropenia occurred during DTX treatment, temporary treatment interruptions were required; however, all cycles were completed with a relative dose intensity of 80%. As stable disease after completion of NAC, right breast-conserving surgery with sentinel lymph node biopsy was performed. Pathological assessment after neoadjuvant chemotherapy revealed ypT1c (1.8 cm) sN0 (0/1), therapeuthic effect Grade 2b, ER- (0%), PgR- (0%), HER2 0, Ki-67 20% of residual tumor remaining in the breast. Therefore, BRACAnalysis® testing was performed as a companion diagnostic test and was negative. The patient subsequently have received postoperative radiotherapy, and 8 cycles of capecitabine therapy. CONCLUSIONS: In our cohort of ILC patients treated at our institution, we also observed cases with gastrointestinal metastases; therefore, attention should be paid to symptoms and findings suggestive of metastasis to these sites as well.