Pathologic findings in nonpalpable invasive breast cancer

Previous studies have shown that patients with nonpalpable invasive breast cancer have a favorable prognosis. These studies, however, have not analyzed pathologic features of mammographically detected tumors according to tumor size. We describe the histopathologic features of 77 nonpalpable invasive breast cancers, comparing neoplasms less than or equal to 1 cm with larger clinically occult tumors. Forty-seven lesions (61%) were less than or equal to 1 cm (group A) and 30 (39%) were greater than 1 cm (group B). In group A, there were 30 infiltrating ductal carcinomas (IDC); seven infiltrating lobular carcinomas (ILC); and two cases each of mixed ILC and IDC, mixed tubular carcinoma and ILC, and infiltrating cribriform carcinoma. There was one case each of mucinous carcinoma, apocrine carcinoma, tubular carcinoma, and mixed mucinous and IDC. In group B, there were 23 (77%) IDC, five (17%) ILC, and two mixed IDC and ILC. Tumors in group B were more frequently grade 3 (22% versus 7%), but this was not statistically significant (p = 0.21). There were no important differences in the frequency, subtypes and location of carcinoma in situ, or other histopathologic parameters evaluated in the biopsy specimens. Mastectomy specimens with axillary lymph node dissections were available for review in 64 cases (83%). Group B patients had a higher rate of residual invasive carcinoma (31% versus 13%) and lymph node metastases (31% versus 16%), but these differences were not statistically significant. Residual carcinoma in situ was more frequent in group B (54%) compared with group A (26%) (p = .036). Of seven group B cases with negative biopsy margins, residual invasive carcinoma was present in five (71%). We conclude that small nonpalpable invasive breast cancers differ from larger nonpalpable tumors primarily in size. The finding of negative biopsy margins should not be construed as conclusive evidence for the absence of residual infiltrating disease.