What is Metastatic Breast Cancer?

Lobular cancers start in the acinus of the lobule, the structure within the glands that produce breast milk. Unlike ductal cancer cells, lobular cancer cells spread through the wall of the acinus into the fat and fibrous tissues of the breast but do not collect scar tissue. They can sometimes grow without forming a mass, making them harder to find.

Inflammatory breast cancer is an aggressive but uncommon form of breast cancer. It can be ductal or lobular. It develops when cancer cells block the lymph vessels in the skin of the breast, causing it to be red, swollen and tender. 

When breast cancer cells invade the wall of the milk duct or acinus, they are called invasive or infiltrating. These cancers have the ability to spread beyond the breast and nearby lymph nodes to the armpit, neck or chest, through lymphatic channels or through the bloodstream.

Doctors put breast cancer into five stages: stage 0, which is considered non-invasive (in situ) and stays within the ducts or lobules, and stages I through IV. All cancers above stage 0 are considered invasive cancers. Stages are based on tumor size, lymph node involvement and whether the cancer has spread beyond the breast and nearby lymph nodes to other parts of the body. When cancer is metastatic, the cancer has traveled away from the breast and lymph nodes to other parts of the body, such as the bones, lungs, liver or brain. Though cancer at any stage can become metastatic, metastatic cancer is the term used to refer to stage IV cancer.

Breast cancer is also broken down by subtype. Subtypes are determined by the cancer cells’ reaction to the hormones estrogen and progesterone, usually recognized by the presence of hormone receptors in the cells (referred to as hormone receptor status), or too much of the HER2 protein, called the HER2 status. Your doctor will also note how the cancer grows (in a sheet or in a mass) and the proliferation index, which tells what percentage of the cancer cells are actively dividing.

Knowing the subtype can help you and your doctors determine the best course of treatment for you. Many targeted medicines have been and are being developed for specific subtypes. All subtypes of breast cancer can become metastatic.

How Breast Cancer Metastasizes

When breast cancer metastasizes, the cancer cells enter the lymphatic channels or the bloodstream and spread to lymph nodes or other organs of the body.

Breast cancer cells can travel away from the breast and get into the blood stream fairly easily, but only a select few can survive and grow in other organs. Typically, your body will reject or attack things it doesn’t recognize (like germs), but in the case of metastasis, cancer cells seem familiar enough that different areas of the body allow them to grow. The most common locations of breast cancer metastases are the liver, bones, lungs and brain.

If you had breast cancer before, this new diagnosis may be referred to as recurrent disease. In this case, some of the primary cancer cells survived the treatments you may have had after your early-stage diagnosis. Systemic therapies like hormonal therapy and chemotherapy aim to eliminate cancer cells in the breast as well as those that may have already started traveling to other parts of the body. But in some cases, those cells escape the treatment and begin to grow later.

Many doctors have researched the process of metastasis, but to date no one can predict how long cancer cells will be inactive before they begin to grow and can be detected.

Even though the cancer cells spread to a different area of the body, your doctors will still treat them as breast cancer. Being diagnosed with bone metastasis is not the same as being diagnosed with bone cancer. Under a microscope, the cancer cells still look the same as breast cancer cells. Though they are growing at a distant site, these cells have many of the same mutations and a similar genetic makeup to the cells that caused the cancer in the breast. If you had early-stage breast cancer before, your doctor may decide to do a biopsy to ensure the tumor cells remain similar to those at your original diagnosis.

If this is your first cancer diagnosis, it is possible your doctors discovered you have breast cancer because you had symptoms in a different area of your body, like your bones. Your doctors were able to make the diagnosis because breast cancer cells remain breast cancer cells, no matter where they are.

Your doctors should run tests to make sure that the cancer cells from the metastatic site are the same as your primary diagnosis (if you had one). They will adjust your treatments if necessary, for the best results possible.

What Makes Metastatic Breast Cancer Different

You may have heard doctors or the media talk about breast cancer as a disease that can be treated and then ends. At the end of treatment for your first diagnosis, maybe you felt your experience was over. Perhaps your doctors mentioned the chance of recurrence, but it sounded unlikely.

There are many people who undergo treatment and never have to deal with cancer again. A metastatic breast cancer diagnosis is different because it means you will actively deal with breast cancer for the rest of your life.

With metastatic breast cancer, the goal of treatment is to shrink or weaken the cancer, manage your symptoms and side effects and prevent the cancer from spreading further. Changes in treatment are made as the cancer grows or spreads to new places in your body. You and your doctors will talk regularly about progression, the growth of tumors or spread of cancer, and regression, decreases in tumor size or the cancer’s reach. When one treatment stops working, you and your doctors will look at new options.

When talking with your doctor, ask about treatment side effects. Maintaining your usual daily activities and being able to participate in the things you enjoy are essential to your overall well-being. It may be helpful to talk openly with your medical team about how symptoms and side effects impact you every day.

Treatment for metastatic breast cancer has two main goals: to control the cancer for as long as possible, with the highest quality of life possible.

At stage IV it is difficult to fully remove cancer with surgery or medicine because new tumors may appear over time, or cells may stop responding to different treatments. While metastatic breast cancer is not considered curable, it is possible to experience periods where tests show no evidence of disease, often called NED. While reaching NED may not always be possible, it is likely that you will have periods when the cancer does not grow. This is called stable disease.

Being diagnosed with metastatic breast cancer can happen to anyone, at any time. Even stage I cancer can become metastatic. Years after completing treatment, someone with stage I cancer may learn the cancer is back and is now metastatic. The stages are meant only to predict your risk of recurrence.

While the main goal is choosing the treatment path that will get rid of tumors and outlying cancer cells in the most effective way, you and your doctors may also want to think about what you are willing to try and what you aren’t, so that you continue living the way you want to live.