<unk>  <unk>  literally means groups of "cancerous" epithelial cells which remained in their normal location (in situ) within the ducts and lobules of the mammary gland. Clinically, it is considered a premalignant (i.e. potentially malignant) condition, because the biologically abnormal cells have not yet crossed the basement membrane to invade the surrounding tissue. When multiple lesions (known as "foci" of<unk>  are present in different quadrants of the breast, this is referred to as "multicentric" disease. For statistical purposes, some count<unk>  as a "cancer", whereas others do not. When classified as a cancer, it is referred to as a non-invasive or pre-invasive form. The National Cancer Institute describes it as a "noninvasive condition".
Ductal carcinoma in situ
Basal cell adenoma
Extramammary Paget's disease
Inverted papilloma
Carcinoma in situ
Lymphomatoid papulosis
Squamous cell papilloma
Lobular carcinoma in situ