Invasive Breast Carcinoma of No Special Type, Microinvasive Carcinoma, Tubular Carcinoma, and Cribriform Carcinoma

Invasive breast carcinoma of no special type (IBC NST) is the most common invasive carcinoma. It is a diagnosis of exclusion conferred when the tumor cannot be classified as a specific type of breast carcinoma. Consistent with the no special type classification, IBC NST shows marked heterogeneity in morphology, grade, hormone receptor (HR) and HER2 expression, and prognosis. Microinvasive carcinoma, defined as invasion 1 mm or less in greatest dimension, is usually found in association with carcinoma in situ and shows an overall prognosis similar to ductal carcinoma in situ. Tubular and invasive cribriform carcinomas are special types of IBC that are low grade, invariably HR positive and HER2 negative, and have an excellent prognosis. Although gene expression profiling has segregated tumors into different subtypes, classification based on morphologic features is invaluable for some of these special types of breast carcinomas as it determines prognosis and guides treatment options.