Tubular carcinoma and grade 1 (well-differentiated) invasive ductal carcinoma: comparison of flat epithelial atypia and other intra-epithelial lesions.

The distinction between tubular carcinomas (TC) and invasive well-differentiated (grade 1) ductal carcinoma (IDC) is important given treatment and prognostic differences. Studies have described a strong association between flat epithelial atypia (FEA) and TC. The incidence of FEA associated with grade 1 IDC is not well established. The aim of the present study was to assess morphology and intra-epithelial lesions between 14 TC and 18 grade 1 IDC matched for size. Of 14 TC, eight (57%) had associated FEA, seven (50%) had micropapillary atypical ductal hyperplasia (ADH), three (21%) had low nuclear grade ductal carcinoma in situ (DCIS), and four (29%) had lobular neoplasia. Notably, only two of 18 (11%) grade 1 IDC had associated FEA. Three of 18 (16%) grade 1 IDC had ADH, two (11%) had lobular neoplasia, and seven (39%) had DCIS. All tubular carcinomas were estrogen receptor (ER) positive and negative for Her-2/neu overexpression. All grade 1 IDC were ER positive but 5% also overexpressed Her-2/neu. Axillary lymph node metastasis was present in 11% of grade 1 IDC and absent in TC. A strong association was found between TC, FEA, and micropapillary ADH, which may reflect a biological progression. Despite matching for tumor size, grade 1 IDC have a higher incidence of lymph node metastasis and may have Her-2-neu overexpression compared to TC.