Mucoepidermoid and squamous cell carcinomas of breast with reference to squamous metaplasia and giant cell tumors.

Clinical and pathologic features of five low-grade mucoepidermoid and a similar number of squamous cell carcinomas of breast are presented. Three of each were retrieved from 55 cases of invasive breast cancer previously assessed to exhibit squamous metaplasia. Although the estimated incidence of low-grade mucoepidermoid cancers is approximately 0.2%, they may be more frequent, masquerading under designations of squamous metaplasia or intracystic carcinomas. All patients with low-grade mucoepidermoid cancer, and the two recorded previously, were free of recurrence for 4-10 years. No high-grade mucoepidermoid cancers were found. Squamous cell cancers frequently have a phyllode configuration (carcinoma phyllodes). Two examined by electron microscopy revealed a commonality of ultrastructural features with similar tumors of other sites. None exhibited glandular differentiation or tinctorial evidence of mucin secretion. One squamous cell carcinoma contained both malignant epithelial and banal, osteoclast-like, stromal giant cells. Only the latter were identified in tissue culture. This experience and review of the literature prompted a nosologic characterization of giant cell lesions of breast. One patient with squamous cell carcinoma succumbed because of her disease; the remainder are either free of or alive with recurrence at 4 and 10 years.