Solid papillary carcinoma of the breast with high-grade cytological features: challenging the concept of indolence

Solid papillary carcinoma (SPC) of the breast is a rare neoplasm typically regarded as a low-grade tumor with indolent behavior. We report two cases of SPC in elderly women presenting with palpable breast masses. Preoperative imaging demonstrated BI-RADS 4 suspicious lesions, and ultrasound-guided core needle biopsy suggested a papillary neoplasm consistent with SPC. Definitive histopathological examination revealed SPC with unusual high-grade cytological features, including marked atypia, increased mitotic activity, and an elevated Ki-67 proliferation index, despite the absence of conventional invasive morphology in one case. These findings highlight a striking discordance between the typically indolent architectural appearance of SPC and cytological indicators of aggressive potential, underscoring the biological heterogeneity of this rare entity. Recognition of these atypical presentations is essential for accurate pathological diagnosis, risk stratification, and appropriate clinical management.