Breast cancer classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Mirdula Sharma, MBBS [2] Soroush Seifirad, M.D.[3]

Overview

Breast cancer may be classified according to anatomy into 4 subtypes: ductal, lobular, sarcoma, and lymphoma.

Classification Based on Histopathology

Malignant Tumors

Type	Subtype
Ductal	Ductal carcinoma in situ (DCIS) Comedo type: ~60% Non-comedo type: ~40% Papillary Micropapillary Cribriform Solid Intracystic papillary carcinoma in situ Invasive ductal carcinoma Invasive ductal carcinoma not otherwise specified (NOS): ~65% Tubular carcinoma of breast: ~7-8% Tubulolobular carcinoma of breast Medullary carcinoma of breast: ~2% Mucinous (colloid) carcinoma: ~2% Malignant papillary lesions of the breast Papillary carcinoma of breast: 1-2% 1
Lobular	Lobular carcinoma in situ (LCIS) Invasive lobular carcinoma: ~10%
Other malignant breast tumors	Inflammatory breast cancer: 1-4% Paget's disease of the breast Triple negative and basal-like breast cancers Metaplastic carcinoma of the breast Adenoid cystic carcinoma of the breast: <0.4% Apocrine carcinoma of the breast
Sarcoma	Angiosarcoma of the breast Fibrosarcoma of breast Extra-skeletal osteosarcoma of breast Malignant phyllodes tumor Angiosarcoma Rhabdomyosarcoma
Lymphoma	Non-hodgkin lymphoma
Metastases to the breast	The most common extra-mammary cancers that metastasise to breast are: Lymphoma/leukaemia: most common extra mammary source Melanoma Sarcomas Prostate cancer: considered on the most frequent primary sites in men 4 Lung cancer Gastric cancer Ovarian cancer Renal cell cancer

Benign Tumors

• Phyllodes tumor
• Mammary fibromatosis: 0.2% of all breast tumors 5
• Benign papillary lesions of the breast

• Papilloma

• Intraductal papilloma
• Solitary papilloma of breast
• Central solitary papilloma of breast
• Peripheral solitary papilloma of breast
• Multiple papillomata of breast

• Juvenile papillomatosis of breast

• Granular cell tumor of the breast

Classification Based on Hormone Receptors Present

• Hormone receptor positive: either estrogen or progesterone receptors are present
• Hormone receptor negative: breast cancer cells don’t have either estrogen or progesterone receptors
• HER2 positive: If excess copies of HER2 gene
• HER2 negative: If excess copies of HER2 gene are not present
• Triple positive: cancers that are ER-positive, PR-positive, and have too much HER2
• Triple negative: If the breast cancer cells don’t have estrogen or progesterone receptors and don’t have too much HER2

Classification Based on Gene Expression

• Luminal type: are estrogen receptor (ER)–positive

• Luminal A:

• Low grade,
• Grows slowly,
• Have the best prognosis

• Luminal B:

• Grows faster