Early Distant Metastasis in Synchronous Bilateral Breast Cancer including a Small Low-Grade Carcinoma with Osteoclast-Like Giant Cells: A Case Report.

introductionBreast carcinoma with osteoclast-like giant cells (OGCs) is an uncommon morphological finding, and its clinical significance remains unclear. We report a case of synchronous bilateral hormone receptor-positive breast cancer including a small, low-grade carcinoma with OGCs, followed by early distant recurrence after surgery. CASE PRESENTATION: A 47-year-old woman presented with a palpable mass in the left breast. Imaging revealed synchronous bilateral breast tumors without evidence of nodal or distant metastasis. She underwent bilateral mastectomy and bilateral sentinel lymph node biopsy. The right breast tumor was a carcinoma with OGCs measuring 6 mm in diameter; it was estrogen receptor (ER)-positive, progesterone receptor (PgR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, had a Ki-67 labeling index of 10%, was nuclear grade 1/histological grade 1, and showed no lymphovascular invasion or nodal metastasis. The left breast tumor was an invasive ductal carcinoma (so-called scirrhous type), measuring 25 mm in diameter; it was ER-positive, PgR-positive, HER2-negative, had a Ki-67 labeling index of 10%, was nuclear grade 2/histological grade 2, showed lymphatic invasion, and had an Oncotype DX recurrence score of 16. Tamoxifen was initiated. CT performed 6 months after surgery as postoperative imaging follow-up for this patient revealed multiple pulmonary nodules, and PET-CT showed pulmonary and lumbar vertebral lesions. Pathological confirmation was not performed; therefore, the precise origin could not be determined. Fulvestrant plus abemaciclib was started for clinically suspected recurrent breast cancer.

conclusionsThis case illustrates that early distant recurrence can occur in synchronous bilateral hormone receptor-positive breast cancer even when available clinicopathological and genomic findings appear relatively favorable. However, because the left conventional invasive ductal carcinoma had more plausible recurrence-risk features than the small right-sided carcinoma with OGCs, and because the metastatic lesions were not pathologically confirmed, this case should not be interpreted as evidence that the OGC-containing carcinoma caused the recurrence. Rather, it highlights the diagnostic and risk-assessment complexity of synchronous bilateral breast cancer that includes a rare stromal-rich morphological pattern.