Invasive carcinoma of no special type (NST) is also referred to as invasive ductal carcinoma or infiltrating ductal carcinoma (IDC) and invasive ductal carcinoma, not otherwise specified (NOS). Each of these terms represents to the same disease entity, but for international audiences this article will use invasive carcinoma NST because it is the preferred term of the World Health Organization (WHO).

Invasive carcinoma NST accounts for half of all breast cancer diagnoses in women and is the most common type of invasive breast cancer. It is also the most commonly diagnosed form of male breast cancer. Invasive carcinoma NST is classified by its microscopic, molecular, and genetic features. Microscopically it is a breast carcinoma originating from the breast ducts that shows invasive features but lacks the "specific differentiating features" of other types of invasive breast cancers. Invasive carcinoma NST is a diagnosis of exclusion, which means that for the diagnosis to be made all the other specific types must be ruled out. There are several rare sub-types of invasive carcinoma NST including pleomorphic carcinoma, carcinoma with osteoclast-like stromal giant cells, carcinoma with choriocarcinomatous features, and carcinoma with melanotic features.

Invasive breast carcinomas are most common in White women, followed by Black and Hispanic women. Black women tend to have greater severity of disease at diagnosis with worse overall survival. Breast cancer is often asymptomatic and diagnosis by screening, but may present with symptoms of pain, palpable mass, skin changes, or complications of metastasis.

Clinical disease or suspicious lesions on screening may evaluated further with tissue sampling. Diagnostic analysis will include histopathological typing, grading, and analysis for DNA markers and receptor-status. The prognosis for patients with invasive carcinoma NST is heterogenous and difficult to predict for every individual. However, general factors such as high tumor grade, stage, receptor negativity, BRCA1-positivity suggest higher risk of recurrence and lower overall survival. Treatment is individualized however most patients are offered some combination of neoadjuvant, surgical, radiation, and adjuvant systemic medical therapies.