What Are the Different Types of Metastatic Breast Cancer?

Defining the Various Terms Associated With Stage 4 Breast Cancer

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The word “metastatic” is used in different ways with breast cancer, so let’s begin by exploring a few definitions of terms you may come across.

Defining "Metastatic"

Metastatic breast cancer is the same thing as stage 4 breast cancer and is considered the most advanced stage of breast cancer. It refers to breast cancers which have spread beyond the breast and nearby lymph nodes to other regions of the body like the bones, liver, brain, or lungs (also referred to as distant metastases).

However, if you’ve read through any of your pathology reports, for example, the written evaluation about a lymph node biopsy you have had, you may have seen the word “metastatic.” Metastases to lymph nodes—the spread of cancer to lymph nodes—does not mean that you have metastatic breast cancer. Rather, lymph node metastases are important primarily because they are a signal that your cancer has the potential to spread or become metastatic.

Cancers can spread in a few ways—through the lymphatic system or through the bloodstream. When breast cancers spread and enter the lymphatic system they usually arrive first at nearby lymph nodes and may still be an early stage breast cancer.

Note that when breast cancer spreads it is still breast cancer. If you were to take a sample of the cancer in these locations and look at it under the microscope, the appearance would be of cancerous breast cells, not bone, liver, or lung cells.

Thus, for example, breast cancer that has spread to the bones is not called bone cancer, but rather “breast cancer metastatic to the bones.”

Advanced Breast Cancer

Your oncologist may use the term “advanced breast cancer” when talking about your tumor, or you may read this term when learning about your cancer.

An advanced stage breast cancer usually refers to breast cancers that are either stage 3B or stage 4 (metastatic).

These tumors are currently not curable, but these cancers are very treatable and treatments can both extend life and lessen the symptoms of cancer. The average survival time with metastatic breast cancer is improving, and there are some people who have survived for a long time after a diagnosis of metastatic breast cancer.

Invasive vs. Non-Invasive

The term invasive breast cancer is frightening, but like metastases to lymph nodes, does not mean that a cancer is metastatic. The term invasive breast cancer refers to any cancer which has spread beyond an area called the “basement membrane.” In fact, the only stage of breast cancer which is not considered invasive is carcinoma in situ or stage 0 breast cancer. Stages IA to stage 4 breast cancer are all considered invasive breast cancer.

Major Types

There are several types of metastatic breast cancer, and within these general categories there are many molecular differences between different cancers.

Breast cancers are first broken down into the major types:

  • Metastatic Intraductal Breast Cancer – Intraductal, or ductal breast cancers are those which begin in the epithelial cells (lining cells) of the milk ducts. This is the most common form of breast cancer, accounting for four out of five cases. There are several subtypes of ductal carcinoma of the breast including tubular, medullary, papillary, and mucinous among others. These can vary in the typical age of onset, the aggressiveness, and much more.
  • Metastatic Intralobular Breast Cancer – Intralobular, or lobular breast cancer arises in the epithelial cells which line the lobules of the lungs which produce milk. This is the second most common type of breast cancer, accounting for around 10 percent of cancers. It tends to occur in older women relative to ductal carcinomas, but this can vary as well.
  • Metastatic Inflammatory Breast Cancer – Unlike most breast cancers, inflammatory breast cancer is often in the advanced stages of the disease at the time of diagnosis. These cancers, which account for around 1 in 100 breast cancers, often appear as redness and swelling in the breast rather than a distinct lump.
  • Paget’s Disease – Paget’s disease accounts for around five percent of breast cancers and arises in the ducts of the nipple. These cancers usually begin with a red, scaly rash on the nipple, and are often associated with an underlying invasive cancer deeper in the breast.
  • Uncommon Types of Breast Cancer – There are several other different types of cancers which can arise in the breast such as phyllodes tumors, sarcomas, and more.

De Novo Cancer

De novo breast cancer refers to breast cancers that are metastatic at the time of initial diagnosis, and accounts for five to ten percent of metastatic breast cancers.

Sometimes, metastases are diagnosed when tests such as a PET scan are done in the process of staging a breast cancer. Less commonly, the sites of metastases are found first, before a breast cancer is diagnosed. For example, a person may have a fracture, and on x-ray metastases may be found in the bone underlying the fracture. The breast cancer may be then found as part of a workup to determine the location of the original cancer.

Recurring Cancer

Most of the time (90 to 95 percent of the time) metastatic breast cancer represents a recurrence of a previous breast cancer.

A recurrence following a primary breast cancer may occur months, years, or even decades following the original tumor. The timing of the recurrence may give your oncologist some important information about your cancer. For example, tumors that recur within three years of the original cancer tend to be more aggressive than tumors which recur later, although again, this is not always the case.

We aren’t certain how cancer cells can “hide” or why they appear again. One theory is that there is a hierarchy among cancer cells, with cancer stem cells being more resistant to the treatments we use for early stage breast cancer. For some reason, these cancer cells survive the treatments we use and lie dormant, waiting to again begin growing at some later point in time.

We do know that breast cancers that are estrogen receptor positive are more likely to recur in the first five years after treatment than those which are estrogen receptor negative.

Sometimes it can be difficult to know whether a recurrence is a true recurrence. It’s thought that cancers which recur in the first three months after treatment are not a true recurrence but rather a progression of the original cancer.

Treatments for metastatic breast cancer are often similar whether it represents a recurrence or a de novo breast cancer, but there are some differences. A tumor which is metastatic at the time of diagnosis may be more aggressive, but this is not always the case. Some types of breast cancer, such as inflammatory breast cancer, are more likely to be found when they are already metastatic.

A Word From Verywell

It’s important to understand that even if two cancers are both ductal breast cancers with the same subtype, there can still be a number of differences. Every breast cancer is unique. In fact, many of the newer treatments for cancer address some of the unique molecular differences between breast cancers.

One of the reasons it’s helpful to understand how every cancer is different is because—if it hasn’t happened already—you will probably begin to hear about others who have faced a “similar” type of breast cancer. Well-meaning friends and family members may share stories of how someone they knew with the same type of cancer as you did with treatment. These stories may be followed by further well-meaning suggestions on how your cancer should be treated.

Even if your neighbor’s third cousin’s ex-husband’s sister had the same type of breast cancer as you do with the same estrogen receptor status, this does not mean that your cancer is the same or will respond to the same treatment.

Every person is different and every cancer is different. Statistics may provide us some information, but many of these statistics were gathered before the newer treatments for metastatic breast cancer were available. You may need to, at times, gently remind your friends that you’re pursuing the treatment you feel is right for you alone. Period.

American Cancer Society. Cancer Facts and Figures 2016. https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/annual-cancer-facts-and-figures/2016/cancer-facts-and-figures-2016.pdf

DeVita, Vincent., et al. Cancer: Principles & Practice of Oncology. Cancer of the Breast. Wolters Kluwer, 2016.

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