Breast cancer is not a single disease but rather a complex group of diseases that behave differently and yield different treatment results. It is, therefore, extremely important to patients and healthcare providers to have an understanding of the different kinds and subtypes of breast cancer because it determines treatment decisions and predicts outcomes. We discuss in this blog some of the types of breast cancer, how they are characterized, and classified.

Frequently Occurring Types of Breast Cancer

Invasive (Infiltrating) Ductal Carcinoma (IDC): IDC is the most common type of breast cancer found in the United States. IDC originates in the milk ducts and eventually breaks through the duct wall and invades the surrounding breast tissue. Moreover, this form of breast cancer can further spread beyond the breast to elsewhere in the body. IDC accounts for about 80% of all diagnosed types of breast cancer.

Lobular Breast Cancer: The second most common form of breast cancer, lobular, begins in the milk-producing glands, or lobules, of the breast. It tends to spread to surrounding breast tissue and may be harder to detect on mammograms than IDC.

Ductal Carcinoma In Situ (DCIS): DCIS is a type of pre-cancer in the lining of a milk duct within the breast, where abnormal cells have developed, but the abnormal cells have not invaded through the walls of the ducts into the surrounding breast tissue. Since it is not invasive, it cannot travel to other parts of the body. DCIS is present in approximately 20-25% of new breast cancer cases.

Less Common Types of Breast Cancer

While the above represent the majority of breast cancer cases, there are a few more less common types of breast cancer that are important to know about:

Triple-Negative Breast Cancer: TNBC, is an aggressive form of invasive cancer, which is characterized by fast growth and quick spread relative to most other breast cancers. The term “triple-negative” has been coined because the cancer cells behave in such a way that they lack estrogen receptors, progesterone receptors, and HER2 proteins to help direct the target of treatment. Treatment for TNBC can also be more aggressive in nature since it has no target for hormonal therapies or HER2-targeted treatments.

Inflammatory Breast Cancer (IBC): This is a rare, aggressive form of breast cancer that presents with redness and swelling in place of a discrete breast lump. It is reported to account for only 1–5% of all breast cancers in the US but to behave very aggressively.

Paget’s Disease of the Breast: This rare form of breast cancer impacts the skin of the nipple and often the areola. It may appear as a rash and is sometimes mistaken for eczema or dermatitis. Paget’s disease accounts for less than 4% of all breast cancers.
In addition to the primary types of breast cancer, health care providers also group the most cancers in the breast based on whether the cells have particular receptors or not. They need this information to determine the best way to take care for the cancer.

Breast Cancer Subtypes

In addition to the main types of breast cancer, healthcare providers further classify breast cancers into subtypes based on the presence or absence of certain receptors on the cancer cells. This classification is crucial for determining the most effective treatment approach.

1. Hormone Receptor Status
   • • ER-positive (ER+): Cancer cells have estrogen receptors.
     • PR-positive (PR+): Cancer cells have progesterone receptors.
     • HR-positive (HR+): Cancer cells have both estrogen and progesterone receptors.
     • HR-negative (HR-): Cancer cells lack both estrogen and progesterone receptors.

   Hormone receptor-positive cancers can often be treated with hormonal therapies that block or lower estrogen levels in the body.

2. HER2 Status

• • HER2-positive (HER2+): These cancers have higher than normal levels of the HER2 protein, which promotes cancer cell growth. About 15-20% of breast cancers are HER2-positive.
  • HER2-negative: These cancers do not overexpress the HER2 protein.

HER2-positive cancers can be treated with targeted therapies that specifically attack the HER2 protein.

Why Classification is Important

It is critical to find out the type and subtype of the breast cancer due to a number of reasons:

Definition of Treatment: Various types and subtypes do preferably have a reactiventype to certain treatment for specific. For example, Hormone receptor-positive cancers, in most cases, have a good reaction to hormone treatment while HER2-positive cancers, two-to-three, benefit more from the use of targeted HER2 treatments.

Prognosis: Some breast cancers, especially TNBC and IBC, are aggressive and have a poor prognosis if diagnosed late in the course.

Research: Proper classification of different types of breast cancers helps invent newer and more focused treatments and enables researchers to understand the disease better.

Personalized Medicine: With treatment regimens custom-formed for the exact type and subtype of breast cancer at hand, the possible outcome is better control and fewer side effects.

Conclusion

The disease is itself complex and there are so many types and subtypes. With that knowledge will come the ability for patients to know more about their personal diagnosis and their treatment options.

Further, research no doubt will continue to delineate breast cancer types and subtypes in a way that sets the stage for even more personalized, effective treatments. If you receive a breast cancer diagnosis or if a loved one does, make sure you talk to your healthcare provider about the specific type and subtype; that knowledge is a powerful tool in your cancer journey.