What is Metastatic Cancer?

Welcome to Turning Cancer on Itself: Metastatic Cancer and Cutting-edge Care, a multi-part blog series about metastatic disease, current therapy and its limitations, and promising new treatment approaches that are entering the clinic. This month, part one focuses on a basic discussion about metastatic disease and what this diagnosis means for patients.

One of the most dreaded words to follow a cancer diagnosis is to hear that the disease has metastasized. This occurs when cancer cells or tumors are detected outside the location where the cancer began. For instance, metastatic cancer might describe a lung cancer that has spread to the liver or a breast cancer that has spread to the brain. For this to happen, a series of complex steps are required. First, cancer cells from the original tumor must gain the ability to access the highways of the body, such as the bloodstream or a set of channels called the lymphatic system. Once on these highways, a cancer cell must invade a new tissue and survive within it. Finally, the cancer cell expands into a colony (called a “metastasis”) by dividing rapidly and building a blood supply. If this sequence is successful, the patient is said to have “metastatic cancer.”

These metastases are sometimes identified on routine diagnostic imaging scans such as CT, PET, or MRI. They can also be found because of symptoms. For example, a metastasis in the liver may cause fatigue, a yellowing of the skin, swelling, or abdominal pain. A brain metastasis may cause seizures, headaches, or other neurological symptoms. In some cases, metastases are detected at the same time as the original cancer. In other cases, the metastases may appear months or years after the original tumor has been treated.

The appearance of a metastasis indicates an advanced state of disease, although prognosis can depend on how far the disease has spread. When these metastases are only found in nearby immune system tissues called “lymph nodes,” the cancer may still be treatable with an aggressive local therapy such as surgery or radiation coupled with drug therapy. On the other hand, when a metastasis is detected in tissues or organs other than nearby lymph nodes, it is labeled a “distant metastasis.” For many kinds of cancer, the appearance of a distant metastasis is considered to be stage 4 disease, and it is associated with a worse prognosis.

Once a distant metastasis is detected, an oncologist may counsel the patient that the cancer is no longer curable, but that the disease may be slowed or halted for a time with treatment, which usually consists of a drug such as chemotherapy. To be sure, the diagnosis of metastatic cancer is a deeply distressing event for cancer patients and their loved ones. This moment usually requires renewed focus on end-of-life decisions and careful consideration of incorporating palliative care or hospice into the treatment plan, if not already in place.

In addition to the personal toll that metastatic cancer takes on individual patients, it also represents a tremendous public health challenge. About 9.6 million cancer deaths occur worldwide every year, and it is estimated that about 9 out of every 10 of these deaths are due to metastatic – not local – disease (1,2). In the United States, cancer will soon outpace heart disease to become the leading cause of death (3). Despite these grim statistics, the last decade of clinical discovery has generated much hope and optimism among oncologists and patients alike. Exciting therapies are emerging to attack metastatic cancer in new ways, and with these treatments, there may be groups of patients with metastatic cancer whose disease can be controlled for years or even cured.

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Look for our next post the week of January 8, 2019, where I will discuss why it is that patients with metastatic cancer do poorly, and how new approaches to therapy have the potential to change these outcomes for the better.

For more frequent updates, please follow me and RefleXion on Twitter: @SeanShirvaniMDand @RefleXionmed.

Thanks for reading our first RefleXion blog post – we are excited to work on this series and welcome any feedback. Please let us know if there are topics you would like to hear about in the future.

References:

1.      WHO Fact Sheet Cancer [Internet]. [cited 2018 Dec 1]. Available from: http://www.who.int/news-room/fact-sheets/detail/cancer

2.      Chaffer CL, Weinberg RA. A perspective on cancer cell metastasis. Science. 2011 Mar 25;331(6024):1559–64.

3.      Weir HK, Anderson RN, Coleman King SM, Soman A, Thompson TD, Hong Y, et al. Heart Disease and Cancer Deaths – Trends and Projections in the United States, 1969-2020. Prev Chronic Dis. 2016 17;13:E157.