Introduction

Metastasis, a term almost exclusively applied to cancer, simply means that additional sites in the body, distant from the original site, now demonstrate the disease-causing agent. While metastasis can be applied to other health conditions, this article will focus on the application of metastasis specific to cancer.

Definition of metastasis

As defined above, metastasis is the movement of a disease-causing agent from a primary location to another location within the body. When specifically referring to cancer, metastasis is the development in a second area of a tumour which was originally found in another location. A better definition of this phenomenon is the movement of cancer cells from one site to another nearby or distant area in the body. ^[1] Typically, metastasis indicates a more aggressive cancer, one that has been present for a longer period of time, a worse outcome, or all three.

Importance of recognizing symptoms and signs

It is important to recognize the symptoms and signs of metastasis because this recognition can lead to a cancer diagnosis or knowledge that a previously diagnosed cancer has worsened. This information will be useful in having informative conversations with the patient and their caregiver about the treatment wishes, including their desire to pursue treatment or not. Whilst some signs may be physically obvious, such as coughing, headaches, or bloating, sometimes, metastasis is not discovered until diagnostic imaging is done. The sooner a metastasis is recognized, the sooner a treatment plan can be implemented. This will aid finding the best results for the type and stage of cancer, thereby helping enhance the patient’s quality of life.

Understanding metastasis

Explanation of metastasis

Metastasis, plainly put, is the most advanced stage of cancer or other physical disease. As already stated above, when a tumour begins in one location and then is found in another location, whether nearby or far away, this is metastasis. Almost all cancers have the ability to metastasize, although some are much more likely to do so than others. The biggest factors in whether or not a cancer will metastasize are the size of the tumour, the type of cells in the tumour, and the location where the tumour first developed. According to the Cleveland Clinic, due to these factors, the tumours that are most likely to metastasise are tumours originating in the breast, lung, prostate, colon, ovary, oesophagus, pancreas, stomach, uterus, and skin. Some other words that can be used in place of metastasis are “stage IV”, “secondary”, “mets'', or “cancer with mets”.

Common sites of metastasis

The metastatic site will vary based on the primary tumour’s type and location. Some cancers have sites which are more common for metastases. This is frequently seen with breast, lung, or prostate cancer. These three cancers tend to have distant spread to the bones and brain. Overall, the bones and brain are two of the most common sites of metastasis but the other most common sites include the adrenal glands (which are situated on top of the kidney), the liver, lungs, lymph nodes (throughout the body), or the peritoneum ^[2] (the membrane lining the abdominal cavity).

How metastasis occurs

Metastasis can occur through several different mechanisms. According to the National Cancer Institute, cancer can spread by direct invasion into the nearby structures. This may include muscles, soft tissues, bones, skin, or other body structures. A second method in which cancer can spread is through the lymph nodes and blood vessels. This can cause the cancer to be moved to more distant locations than the first mechanism. Once the cells have established a population in the new area, they will develop a new blood supply and begin to increase in size in this new metastatic site. In addition, according to the American Cancer Society, the new metastatic deposit must also develop a way to avoid the immune system’s recognition.

Symptoms of Metastasis

The symptoms of metastasis will depend on both the primary tumour and the location in which the metastasis is found. However, the most straightforward explanation for the kind of symptom experienced is related to normal functioning of the organ. For instance, in the case of a lung metastasis, someone may experience shortness of breath or coughing. Or in the case of a brain metastasis, they may experience a headache or visual changes. 

General symptoms

In general, one may have a sudden, unusual, and unplanned weight loss, night sweats, or a decrease in energy levels which may be severe. These can all indicate metastasis.

Fatigue

A common symptom of cancer is fatigue. However, if it becomes so noticeable that one can no longer complete their daily activities, this may indicate that the cancer has worsened. Cancer cells require a great deal of energy to grow and multiply. This is very draining on the body’s resources. Some cancers may make various chemicals to increase or decrease the function of the immune system while others may stop the production of normal bodily chemicals, such as calcium or potassium. Finally, according to Cancer Research UK, specific physical symptoms such as shortness of breath or bloating may cause increased tiredness because one cannot breathe deeply.

Weight loss

Weight loss can occur for a couple of reasons. These include both eating less and increased energy being used by the cancer cells. Individuals may become full quicker when eating if there are metastatic tumours present in the abdomen, intestines, or liver. There are also several physiological reasons why one may lose weight and these include constipation, anxiety/ emotional distress, and pain. Any or all of these three may lead to a decreased food intake and weight loss. Finally, cancer is a inflammatory process and certain chemicals may be released that lead to weight loss and changes in appetite or metabolism.

Loss of appetite

Similar to what was described regarding weight loss, the tumour may cause appetite loss in a couple of different ways. Again, these would include physical reasons (constipation or pain), psychophysical reasons (pain, anxiety, emotional distress), and systemic reasons (inflammation). Any of these could single handedly cause a loss of appetite, but it is more likely that multiple factors will be occurring at any one time.

Symptoms based on affected organs

As mentioned above, physical symptoms can be associated with the usual structure and function of the affected organ. The most common metastatic symptoms by site include:

Bone metastasis

• Bone pain
• Fractures

Lung metastasis

• Unable to catch your breath
• Coughing

Liver metastasis

• Yellowing in the skin and whites of the eyes
• Swollen belly
• Decreased appetite
• Feeling full more quickly when eating

Brain metastasis

• Headaches
• Dizziness
• Double or blurry vision
• Seizures
• Speech difficulties

Lymph node metastasis

All of the following symptoms are only noticeable on physical examination if the lymph node is near the surface of the skin. While these same symptoms might be present in deeper, more internal lymph nodes, this will not be noticeable except on an imaging exam.

• Swelling
• Firm to the touch
• Hard
• Pain (typically if the tumour in the lymph node is obstructing blood flow)
• Redness (typically if the tumour in the lymph node is obstructing blood flow)

Other symptoms to watch for

Sometimes there may not be any physical symptoms present. This may lead to the metastasis going unnoticed until the individual has routine blood work or an imaging exam. One indicator of metastasis on blood results might be an elevated test for liver function. If the high value is significantly above normal, a thorough exam will be conducted to determine if this is due to a new tumour deposit or another cause.

Signs of Metastasis

Physical signs

The signs of metastasis are very similar to the symptoms. Typically, the symptom can be thought of as an abnormality in the normal functioning of the body site where the metastasis is located. These include pain, swelling (including enlarged lymph nodes), or discoloration (red or yellow). 

Abnormalities on physical examination

Breathing may be difficult or one may become full more quickly when eating. They may have yellowing of their skin or eyes if their liver is affected. If they have brain involvement, they may complain of headaches, blurry vision, or may not be able to speak normally (slurred speech, difficulty thinking of the word they want to use). If a lymph node is involved, this will likely be felt as a firm, tender lump.

Imaging findings

Several different methods of imaging tests are used to evaluate cancer. These include x-rays, CT scans, MRIs, and PET scans. While each test looks at the body in slightly different ways, they can each show tumours and metastatic sites. Based on the tumour type and location, the doctor will order the test that is most appropriate.

Importance of Early Detection

Early detection is important because this can affect treatment decisions. Quality of life also becomes a bigger issue in more advanced settings.

Impact on treatment options

The earlier a metastasis is diagnosed, the more targeted treatment can be. For instance, in metastatic colon cancer with metastasis to the liver, treatment can be directed at the liver. Targeted treatments are also becoming more available and may be more effective when there are less metastatic sites to treat. In general though, once a cancer has become metastatic, it is considered incurable and treatment is no longer given with an intent to cure the patient but to manage their symptoms and extend their life.

Improved prognosis

Similar to what was mentioned regarding treatment given to cure, once a cancer has become metastatic, it is considered incurable. The prognosis is generally poor and treatment is given with the intent of comfort and symptom management.

Quality of life considerations

Quality of life is of great importance when one has been diagnosed with cancer but even more so when the cancer has been classified as metastatic. The patient should have a comprehensive discussion with their medical team to determine their goals for treatment and how they would like to feel and participate in their life now that they have advanced cancer. 

Summary

Metastatic cancer means that cancer has now spread to other parts of the body from where it initially started. This can be found in a physical examination if symptoms are present but symptoms may not always be present depending on where the metastatic site is located. Signs and symptoms must be recognised as early as possible since this can affect treatment options and the overall quality and length of life.