Answer: Infiltrating pleomorphic lobular carcinoma with treatment effect

Histology: The dermis and subcutaneous tissue is replaced by sheets of infiltrative cells arranged in single cords and nests. The individual cells have high nuclear-to-cytoplasmic ratios with scant, eosinophilic cytoplasm, and abundant mitotic figures. Foci display marked nuclear pleomorphism with nuclear hyperchromasia, degenerative atypia, and vacuolated cytoplasm. No in situ epidermal or breast lesions are seen. Immunostains performed on the original core biopsy show the lesion to be positive for AE1/AE3, negative for E-cadherin, and to have a brisk Ki67 proliferation index.

Discussion: Pleomorphic lobular carcinoma has a lobular phenotype, characterized immunohistochemically by the loss of membranous E-cadherin immunolabeling or cytoplasmic p120 catenin labeling, but displays more nuclear pleomorphism, atypia and mitoses than the classic infiltrating lobular carcinoma. Pleomorphic lobular carcinoma has a worse prognosis than classic lobular carcinoma. In addition, whereas the presence of conventional lobular carcinoma in situ (LCIS) is not mentioned at the margins of surgical excision, the presence of pleomorphic LCIS should be documented.

The degree of atypia seen in the markedly pleomorphic cells with cytoplasmic vacuolization is attributable to the neoadjuvant chemotherapy that this patient received before surgery. These wild cells are not characteristic of pleomorphic lobular carcinoma. In resections taken after neoadjuvant therapy, the degree of residual viable tumor should be documented in the surgical pathology report. For instance, the size of the residual tumor should be documented with a description, such as “scattered tumor cells over a predominantly fibrotic area measuring 2 cm” versus “completely viable tumor with minimal treatment effect, measuring 2 cm.” The degree of pathologic response to chemotherapy is prognostic. By extension, the presence of any signs of treatment effect should also be documented in lymph nodes resected after neoadjuvant therapy. For instance, the the presence of histiocytes or fibrosis in a lymph node might represent treated/regressed tumor and should be mentioned.

Reference(s):
– Orvieto E, Maiorano E, Bottiglieri L, et al. Clinicopathologic characteristics of invasive lobular carcinoma of the breast: results of an analysis of 530 cases from a single institution. Cancer. 2008 Oct 1;113(7):1511-20.