Breast Cancer Subtypes and Classification

Breast cancer is a heterogeneous disease, meaning it encompasses a wide range of distinct biological characteristics. Classification systems aim to categorize these variations, aiding in prognosis and treatment selection.

Invasive vs. Non-Invasive Carcinoma

A fundamental distinction lies between invasive and non-invasive forms. Invasive carcinomas have spread beyond the milk ducts or lobules, while non-invasive carcinomas remain confined to their origin. Non-invasive forms include ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).

Molecular Subtypes

Molecular subtyping analyzes the expression of specific genes and proteins within the tumor cells, revealing distinct biological profiles with varying clinical behaviors and responses to therapy.

Luminal A

Characterized by estrogen receptor (ER) and/or progesterone receptor (PR) positivity, and HER2 negativity. Often associated with a favorable prognosis.

Luminal B

Also ER and/or PR positive, but frequently HER2 positive or exhibits high proliferation rates (Ki-67). Generally associated with a more aggressive course than Luminal A.

HER2-Enriched

Defined by overexpression or amplification of the HER2 gene, leading to increased cell growth and proliferation. Often treated with HER2-targeted therapies.

Basal-like

Typically ER and PR negative, HER2 negative, and often associated with a higher risk of recurrence and poorer prognosis. Frequently demonstrates a more aggressive clinical behavior.

Triple-Negative Breast Cancer (TNBC)

A subtype lacking ER, PR, and HER2 expression. It is often more aggressive and has limited targeted treatment options, relying primarily on chemotherapy and other systemic therapies.

Other Classification Systems

Beyond molecular subtypes, other classifications consider factors such as tumor grade (a measure of how abnormal the cells look under a microscope), tumor size, lymph node involvement, and the presence of distant metastases.

The complexity of breast cancer necessitates a multi-faceted approach to classification, combining molecular, histological, and clinical characteristics for optimal patient management.