IntroductionSolid papillary carcinoma (SPC) constitutes a rare variant of papillary breast neoplasms, accounting for fewer than 1% of cases, with nipple-confined in situ SPC representing an exceptionally uncommon presentation [1].This condition primarily affects elderly women, most frequently manifesting as nipple discharge (including bloody secretion) or palpable breast masses[2-3]. Previous studies have demonstrated that conventional imaging modalities, including breast ultrasonography and mammography, lack specificity for SPC diagnosis, making clinical identification challenging[4]. In contrast, breast MRI exhibits superior diagnostic specificity, with SPC characteristically demonstrating high signal intensity on T2-weighted imaging, suggesting possible mucin content - a feature rarely observed in other malignant breast tumors. Nevertheless, definitive diagnosis of SPC requires pathological confirmation, and preoperative core needle biopsy or intraoperative frozen section examination can provide critical histological evidence to guide surgical decision-making[5-6].SPC is pathologically characterized by predominantly intraductal solid expansile growth patterns associated with mucin production and neuroendocrine differentiation [7]. This low-grade tumor demonstrates fibrovascular cores and exhibits indolent biological behavior. The perivascular tumor cells typically arrange in palisading or pseudorosette formations, though some fibrovascular cores may be inconspicuous under microscopic examination. Histologically, the tumor cells show remarkable uniformity with minimal atypia and well-defined cell borders. The cellular morphology varies from oval to spindle-shaped or plasmacytoid, featuring eosinophilic, finely granular or clear cytoplasm. The nuclei display low to intermediate nuclear grade with rare mitotic figures. Intracellular and extracellular mucin deposition may be observed, occasionally forming acellular mucin pools[8-9].