Understanding The Different Types Of Breast Cancer: What Sets Them Apart

The different types of breast cancer represent a puzzle, with the main differentiating factors being the cell of origin, nature, and treatment response. In order to make a timely diagnosis and prescribe a personalised treatment, it is necessary to understand such distinctions. Breast cancer is mainly classified depending on the area from which it starts, and also on whether it has recurred or not, as well as the existence of particular receptors in the cancer cells.

Non-Invasive (In Situ) Breast Cancer

The non-invasive breast cancers are those in which the cancerous cells have gathered in the place where they initially arose and thus have not spread to the adjacent tissues. One of the most common examples is Ductal Carcinoma in Situ (DCIS) that comes from the milk ducts.

However, if DCIS is left untreated, it may heighten the risk of invasive breast cancer development. Besides, there is Lobular Carcinoma in Situ (LCIS), which is localised in lobules. In contrast to DCIS, LCIS hardly turns into invasive but it is a sign of cancer rising in both breasts at a later time. 

Invasive (Infiltrating) Breast Cancer

The invasive breast cancers are the ones that have moved beyond their original site into adjacent breast tissue. The most common type of invasive breast cancer is the Invasive Ductal Carcinoma (IDC), which roughly 70–80% of all breast cancer cases are made up of. IDC insinuates itself into the tissue surrounding the milk ducts.

Invasive Lobular Carcinoma (ILC) is the next major class after the former, making up 10–15% of cases. ILC is formed in the lobules and usually manifests as thickening instead of a clear lump, hence making it difficult to locate using imaging methods. 

Subtypes Based on Receptor Status

Estrogen, progesterone, and HER2 are the names of the receptors that may be found on the surface of breast cancer cells. Thus, the presence or absence of these receptors will affect cancer growth as well as response to therapy. 

Luminal A: These cancer cells show hormone receptor-positivity (estrogen and/or progesterone receptors) and are HER2-negative. The tumours tend to be slow-growing with a good prognosis, and they are often sensitive to hormone therapies.

Luminal B: These tumours resemble Luminal A but might be HER2-positive or have a higher proliferation rate. Compared to Luminal A, they are more aggressive and may need further treatments in addition to hormone therapy.

HER2-Positive: One of the reasons for these types of cancer to grow rapidly is the overexpression of the HER2 protein. However, they respond well to targeted therapies that specifically target the HER2 protein, thus making the treatment effective.

Triple-Negative Breast Cancer (TNBC): A TNBC tumour does not express estrogen, progesterone, and HER2 receptors and is therefore more aggressive and difficult to treat. TNBC represents approximately 10–20% of all breast cancers and is more frequent in young women and those carrying the BRCA1 gene mutation. 

Rare and Aggressive Forms

This consists of some uncommon and more aggressive types of breast cancer: 

Inflammatory Breast Cancer (IBC): It is a rare form that rapidly spreads, causing the breast to change to red, swollen, and warm, the symptoms of inflammation. It is therefore a type that requires urgent intervention. 

Paget Disease of the Nipple: Milk ducts get affected by this condition, and the skin of the nipple and areola that is next to it is the other area into which it spreads. Besides, it is often linked with DCIS or invasive cancer underneath the nipple.

Metastatic Breast Cancer: This term is sometimes interchangeable with Stage IV cancer and refers to the kind that has spread to body parts that are not the breast, for example, bones, liver, lungs, or brain. It is a cancer that, although it cannot be cured, can be controlled by continuous treatment.

Breast cancer is a family of kinds and subtypes, each having its own features and reaction to treatment. Personalised treatments have become possible due to progressive medical research, which has eventually led to the improvement of patients' survival rates. The knowledge of breast cancer's different types and performing regular screening checks are both necessary for effective management and treatment.

Authored by Dr Tushar Patil, Senior Consultant - Medical Oncologist, Sahyadri Super Speciality Hospital, Deccan Gymkhana, Pune. Views expressed by the author are their own.