Types of breast cancer

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Types of Breast Cancer: A Comprehensive Overview

Breast cancer is a highly heterogeneous disease, characterized by a variety of histological and molecular subtypes, each with distinct biological features, clinical behaviors, and responses to therapy. Understanding these subtypes is crucial for accurate diagnosis, prognosis, and treatment planning.

Histological Types of Breast Cancer

Invasive Ductal Carcinoma (IDC)

Invasive ductal carcinoma, not otherwise specified (IDC NOS), is the most common type of breast cancer, accounting for approximately 75% of all cases. IDC NOS is characterized by its ability to invade surrounding breast tissues and its diverse molecular profiles, which include luminal, basal-like, and HER2+ subtypes .

Invasive Lobular Carcinoma (ILC)

Invasive lobular carcinoma represents about 10-15% of breast cancers. It is known for its unique growth pattern, often described as "single-file" infiltration of cancer cells. ILC frequently shows inactivation of the CDH1 gene and is typically estrogen receptor (ER) positive and progesterone receptor (PR) positive, which influences its treatment and prognosis .

Special Histological Types

Special histological types of breast cancer account for up to 25% of all invasive breast cancers and include a variety of subtypes, each with unique pathological and clinical features:

Mucinous Carcinoma: Characterized by the presence of mucin-producing cancer cells, mucinous carcinoma generally has a favorable prognosis and is often ER/PR positive .
Tubular Carcinoma: Known for its well-formed tubular structures, this subtype is associated with an excellent prognosis and is typically ER/PR positive .
Medullary Carcinoma: This subtype is notable for its high-grade features and lymphocytic infiltration. Despite its aggressive appearance, it often has a better prognosis than other high-grade cancers and is frequently ER/PR negative .
Adenoid Cystic Carcinoma: Rare and typically low-grade, this subtype is characterized by the t(6;9) MYB-NFIB translocation and has a relatively good prognosis .
Secretory Carcinoma: This rare subtype consistently harbors the t(12;15) translocation, leading to the formation of the ETV6-NTRK3 fusion gene, and generally has a favorable outcome .

Molecular Subtypes of Breast Cancer

Luminal Subtypes

Luminal A: Characterized by high expression of ER-related genes and low proliferation rates, Luminal A cancers have the best prognosis and respond well to hormonal therapies.
Luminal B: These cancers also express ER-related genes but have higher proliferation rates and may express HER2. They have a slightly worse prognosis than Luminal A and may require additional chemotherapy.

HER2-Enriched

HER2-enriched cancers are characterized by overexpression of the HER2 gene and have a more aggressive clinical course. Targeted therapies such as trastuzumab have significantly improved outcomes for this subtype.

Basal-like

Basal-like cancers, often triple-negative (lacking ER, PR, and HER2 expression), are associated with a poor prognosis and limited treatment options. They are more common in younger women and those with BRCA1 mutations.

Clinical Implications and Prognostic Factors

The histological and molecular classification of breast cancer has significant implications for prognosis and treatment. For instance, special histological types like tubular and mucinous carcinomas are associated with better outcomes, while more aggressive subtypes like inflammatory and medullary carcinomas require more intensive treatment .

Prognostic Markers

Key prognostic markers include tumor size, lymph node involvement, and the presence of specific genetic alterations. The Nottingham grading system, which evaluates nuclear pleomorphism, gland formation, and mitotic count, is widely used to assess tumor grade and predict outcomes.

Conclusion

Breast cancer encompasses a wide range of histological and molecular subtypes, each with unique characteristics and clinical implications. Understanding these subtypes is essential for personalized treatment and improving patient outcomes. Advances in molecular profiling continue to refine our understanding of breast cancer, paving the way for more targeted and effective therapies.