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.
Epidemiology
Invasive carcinoma NST is one of the most common types of all breast cancers, accounting for 55% of breast cancer incidence. Of the invasive breast cancers, invasive carcinoma NST accounts for up to 75% of cases. It is also the most common form of breast cancer occurring in men, accounting for 85% of cases.
The incidence of ductal carcinomas as a whole is 86.3 cases per 100,000 women, with the incidence increasing sharply for women over 40 years of age and peaking at 285.6 cases per 100,000 for women between 70 and 79. This incidence has decreased slightly over time. Incidence of diagnosed cases is highest among White and non-Hispanic women, followed by Black and Hispanic women.
Terminology
Invasive carcinoma NST is a type of breast cancer. It is one of the invasive breast cancers that originates from the breast ductal system, so that it is a type of ductal carcinoma. A defining feature of this ductal carcinoma is that it lacks the "specific differentiating features" of other types of ductal carcinomas. It is important to note that IDC, invasive ductal carcinoma NOS, and invasive carcinoma NST all refer to the same type of breast cancer. For consistency and to serve an international audience, this article will use invasive ductal NST.
The terminology of invasive carcinoma NST has undergone change since 2012. Differing opinions within the medical and public health communities have led to some variance in how this disease is referred in research and clinical settings.
In 2012 the International Agency for Research on Cancer (IARC), a sub-department of the WHO, published the 4th edition of the WHO Classification of Tumors of the Breast. Previously known as 'invasive ductal carcinoma, not otherwise specified', these most recent guidelines advocated for the use of 'invasive carcinoma of no special type'.
There are, however, differing opinions and practices. The research literature continues to use IDC or invasive ductal carcinoma NOS, and some medical textbooks have offered support for continued use of IDC or invasive ductal carcinoma NOS.