A comparison of cell cycle markers in well-differentiated lobular and ductal carcinomas

Infiltrating lobular carcinoma (ILC) and infiltrating ductal carcinoma (IDC ) are similar in many respects and their histologic features occasionally o verlap. Despite the many similarities, some clinical follow-up data and the patterns of metastasis suggest that ILC and IDC are biologically distinct. Unfortunately, most breast cancer research has focused almost exclusively on the ductal subtype or has not stressed the biologic or molecular genetic distinctions between breast carcinoma subtypes. Several reports have sugge sted the possibility that ILCs and IDCs differ with respect to expression o f antigens involved in proliferation and cell cycle regulation. Therefore, we undertook an immunohistochemical evaluation of cell cycle related antige ns in ILCs, including histologic variants thought to represent aggressive n eoplasms, and IDCs matched for histologic grade (Modified Bloom-Richardson Grade I). We believe that different antigent expression profiles could eluc idate the biological distinctiveness of breast carcinoma subtypes and possi bly provide diagnostically relevant information. We studied the expression of the following antigents in 28 archived, formalin-fixed ILCs and 34 well- differentiated IDCs: estrogen receptor (ER), progesterone receptor (PR), He r 2-neu, mib-1, cyclin D1, p27, p53, mdm-2 and bcl-2. 94% of ILCs and 100% of IDCs expressed ER; 75% of ILCs and 76% of IDCs expressed PR; 4% of ILCs and 13% of IDCs expressed c cerb B-2; ILCs and IDCs both expressed mib-1 in approximately 10% of lesional cells; 82% of ILCs and 54% of IDCs expressed cyclin D1; 90% of ILCs and 83% IDCs expressed p27 strongly; 4% of ILCs and 4% of IDCs expressed p53, 25% of ILCs and 33% of IDCs expressed mdm-2; 96% of ILCs and 100% of IDCs expressed bcl-2. None of the apparent differences were statistically significant. The ILC variants demonstrated immunophenot ypes that were essentially similar to ILCs of the usual type. We conclude t hat ILCs and well-differentiated IDCs show similar proliferation and cell c ycle control antigen profiles. Despite their unusual histologic features, m ost ILC variants appear to maintain a characteristic ILC immunophenotype.