Solid papillary carcinoma of the breast: a pathologically and clinically distinct breast tumor.

Solid papillary carcinomas are tumors morphologically characterized by round, well-defined nodules composed of low-grade ductal cells separated by fibrovascular cores. These tumors are rare and affect predominantly older women. Although they are considered in situ carcinomas, debate and uncertainty still exist regarding their true nature, because immunohistochemistry for myoepithelial cells has shown absence of myoepithelial cell layer along the epithelial-stromal interface of the tumor in many cases. Clinically, these tumors present as a palpable, centrally located mass or as bloody nipple discharge. Pathologically, solid papillary carcinomas exhibit low-grade features, and often the tumors display neuroendocrine and mucinous differentiation. In the majority of cases an associated invasive carcinoma is present, with colloid and neuroendocrine carcinomas being the most common. The pathologic differential diagnosis is broad and ranges from benign to malignant lesions. The treatment for solid papillary carcinomas is surgical excision. When invasive carcinoma is not present, the prognosis is excellent.