Indolent Yet Intriguing: High-grade Solid Papillary Carcinoma of the Breast

Breast Solid Papillary Carcinoma (SPC) is an uncommon malignancy that primarily affects elderly women, with an incidence of 1-2%. It is morphologically characterised by well-defined nodules with low-grade nuclear features, which are associated with fibrovascular cores and neuroendocrine development. Although SPC can be invasive or in-situ, the prognosis is generally quite good. Its morphology can mimic several precancerous conditions, leading to frequent misdiagnosis. Distinguishing this tumour from its various morphological equivalents is more straightforward when an appropriate Immunohistochemistry (IHC) panel is utilised. A 45-year-old woman presented with a retroareolar mass in her right breast. Sono-mammography revealed a firm, incompressible mass with irregular borders, calcifications, cystic changes, and necrosis. A right-side simple mastectomy was performed, and the tumour was diagnosed as triple-negative high-grade SPC of the breast with focal invasion. The tumour's origin was ruled out, and the diagnosis was confirmed by a prominent histopathologist. This report discusses a case of SPC, emphasising invasion patterns and evaluating previous knowledge.