20th June 2023

Precursor lesions and Malignant lesions

Breast cancer arises from the epithelial cells lining the terminal duct lobular unit. The development of invasive breast cancer is thought to be due to a multistep process. Lobular carcinoma in situ, atypical ductal hyperplasia, ductal carcinoma in situ (DCIS) and microinvasive carcinoma are described as precursor lesions by the modified WHO classification of breast cancer. DCIS accounts for 3-5% of palpable breast cancer and is seen as widespread or unifocal microcalcification on mammography. DCIS has variable potential for development into an invasive disease and is defined as the proliferation of malignant-appearing mammary ductal epithelial cells without evidence of invasion beyond the basement membrane. Broadly, there are five subtypes of DCIS: comedo, solid, cribriform, micropapillary and papillary. Treatment of DCIS is aimed at preventing local recurrence, particularly of invasive cancer. Treatment options include surgery alone, or surgery followed by radiotherapy and hormonal therapy. With mammographic follow-up, breast-cancer disease-free survival in DCIS approaches 100%.

Invasive ductal carcinoma accounts for 70-80% of all invasive carcinoma whereas invasive lobular carcinoma represents 10-15%. Medullary cancers tend to affect younger patients while colloid/mucoid tend to affect the elderly. 60-70% of breast cancers are oestrogen receptor positive conveying better prognosis. Overexpression of HER2 (growth factor receptor gene) is associated with aggressive disease and poor prognosis. 15% of breast cancers lack the expression of oestrogen, progesterone and HER2 receptors (often referred to as triple-negative breast cancer) and are associated with a high rate of local and systemic recurrence.