Invasive Solid Papillary Carcinoma of the Breast Initially Diagnosed as Invasive Ductal Carcinoma: A Case Report

Solid papillary carcinoma of the breast is a rare papillary neoplasm with distinctive morphology and frequent neuroendocrine differentiation. However, when an invasive component is sampled in a limited core needle biopsy specimen, its solid and nested architecture may mimic invasive ductal carcinoma. We report a case of invasive solid papillary carcinoma of the breast that was initially diagnosed as invasive ductal carcinoma and was ultimately confirmed by comprehensive histopathological and immunohistochemical evaluation.

A 53-year-old woman was referred to our hospital for treatment of right breast cancer detected by screening. Ultrasonography showed a 1.3-cm mass in the upper outer quadrant of the right breast. CT showed no distant metastasis, and breast MRI showed no apparent intraductal extension. The clinical stage was cT1N0M0, stage I. Core needle biopsy at the referring hospital was interpreted as invasive ductal carcinoma. Pathological review at our institution showed relatively uniform epithelial cells arranged in small nests and solid structures. The tumor was strongly positive for estrogen receptor and progesterone receptor, negative for human epidermal growth factor receptor 2, showed a low Ki-67 labeling index of 5%, and was positive for synaptophysin, suggesting invasive solid papillary carcinoma with neuroendocrine differentiation. The patient underwent breast-conserving surgery and sentinel lymph node biopsy. The resected specimen confirmed invasive solid papillary carcinoma. Postoperative Oncotype DX testing showed a recurrence score of 4. Adjuvant chemotherapy was omitted, and the patient received postoperative radiotherapy followed by endocrine therapy with anastrozole. She remains free of recurrence 1 year after surgery.

Invasive solid papillary carcinoma can mimic invasive ductal carcinoma on core needle biopsy. Careful morphological assessment combined with appropriate immunohistochemical evaluation is essential for an accurate diagnosis. In the present low-risk luminal case, adjuvant chemotherapy would probably not have been indicated even if the lesion had remained classified as invasive ductal carcinoma of no special type; however, preoperative recognition of this special subtype may still be clinically relevant for biopsy planning, axillary staging, surgical margin planning, and consideration of minimally invasive local treatment.