Ask an expert: What is oligometastatic cancer?

Oligometastatic cancer is a form of metastasis in which cancer cells have spread to a limited number of different sites in the body. If your cancer has become oligometastatic, recent clinical oncology advances could mean that these new sites of tumours may be treatable with local therapies including radiotherapy. Here, Dr Crispin Hiley, a highly esteemed consultant clinical oncologist, provides expert insight into oligometastatic cancer, explaining what exactly is oligometastatic cancer, how it is diagnosed and evaluated, and what is the prognosis, among other interesting points. 

What is oligometastatic cancer?

Oligometastatic cancer is a term used to define cancers that have spread outside of the original (primary) site where the cancer might have been (whether that is lung cancer, breast cancer, or a colon cancer) to a small number of metastatic sites. 

Often, oligometastatic cancer is grouped according to how many metastases patients have, which might be a single isolated metastasis, three or fewer metastases, five or fewer metastases, etc. At the extreme end of the definition, some use this term to define cancers that have 10 metastases or fewer. 

Despite this, the best definition for oligometastatic cancer at present refers to patients with metastatic disease, with five or fewer sites of cancer in other organs. This can be bone metastasis, liver metastasis, or brain metastasis; the aim is to distinguish this cohort of patients with a small number of metastatic sites from patients who have widespread metastatic disease with cancer in many different sites. This is because it is believed that, even if both groups of patients have what is commonly referred to as stage 4 cancer, the treatment for the two scenarios is different. 

What are the known main causes?

It is unknown why some patients will have cancer that only spreads to one or two sites and other patients will have widespread cancer. 

There is a lot of research currently underway to try and understand why tumours behave differently despite appearing (to all intents and purposes) very similar under the microscope but why in one patient they will only spread to one or two sites and in another patient, they will spread to various sites (more than five or even more than 10). 

A lot of emphasis has been placed on this aspect of oligometastatic cancer, because it is believed that despite patients having advanced cancer (stage 4 with five or fewer sites of metastatic disease), the overall survival for patients can be extended and in a small proportion, perhaps even cured. This would only be achieved, however, following treatment with both chemotherapy and local therapies (either surgery, radiation, or radiofrequency ablation), which are applied directly to the different metastatic sites to control the cancer.

Are there any related risk factors?

Although metastatic cancer has general risk factors including smoking and diet that are associated with the majority of cancer types, there is nothing that appears to be a risk factor specifically for oligometastatic cancer. In this sense, the related risk factors for oligometastatic cancer are more about how a particular cancer behaves and whether the cancer spreads to a small number of metastatic sites (five or fewer) or whether it becomes polymetastatic cancer, which spread to many different sites. 

How is it detected exactly?

Whenever a patient receives a cancer diagnosis, the medical team will always perform a staging, which involves a series of scans and investigations to determine how much the cancer has spread. Generally, this includes a CT scan or a PET scan, which is very good at finding sites of metastatic disease within the body, but often, imaging of the brain (best done with an MRI scan) will also be performed to look for metastatic disease within the brain. 

Overall, oligometastatic cancer detection involves closely examining the patient, defining where the cancer is, and - if a patient has stage 4 cancer and it has spread – determining where exactly the metastasis has occurred (if it is only in one site, for example, the liver or in numerous sites including the bone, lung and beyond). The process is a combination of the initial diagnosis of the cancer itself, which is often carried out with a biopsy, and then proper staging using a PET scan and an MRI scan of the brain. 

What is the prognosis, and is it curable?

At the moment, there is a lot of excitement in the medical community around the management of oligometastatic cancer. There have been several trials combining local therapies with chemotherapy that have been shown to extend overall survival. So, for example, if a patient with lung, breast, or colon cancer (and other cancer types) has a cancer that has spread to the liver and a couple of bone metastasis, these sites can be treated with a combination of different treatment options (surgery and radiotherapy) or with a single modality of treatment (radiotherapy alone). These local treatments may be given alone or in combination with chemotherapy or immunotherapy. 

A very good treatment for multiple metastatic sites involves stereotactic radiotherapy, which can be used to treat cancer that has metastasized to the bones, the liver, the adrenal glands, and the lungs, in particular. Other forms of stereotactic radiosurgery can be used to treat metastatic disease in the brain. So, patients with oligometastatic cancer can be treated with stereotactic radiotherapy alone or sometimes, with a combination of stereotactic radiotherapy and surgery or radiofrequency ablation. 

A different circumstance can occur if there is a synchronous oligometastatic disease, which is a term employed when patients develop an untreated primary cancer but already has metastatic cancer in one or two different sites at the same time. Again, this is a treatment paradigm quite commonly managed in cases of colon cancer, in which patients will often present with a single liver metastasis. In this scenario, surgery will remove the colon cancer and the liver metastasis as well. 

This treatment paradigm has also started to expand to other cancer types such as lung cancer, breast cancer, and rare cancers like sarcoma, for patients with less than five metastatic sites. In these instances, both the primary cancer and the oligometastatic sites are managed with a combination of stereotactic radiotherapy and other treatment options, all of which aim to improve overall survival for patients at the very least, and in a small proportion, perhaps cure them. 

From clinical trials (one of them called the SABR-COMET trial), we know for certain that patients who adopt an aggressive approach to the management of oligometastatic disease with local therapies (for example, stereotactic radiation) have better outcomes than others who do not. In the SABR-COMET trial, in particular, approximately half of the patients in the trial were still alive five years after treatment when they had radiation and stereotactic radiotherapy for their oligometastatic disease, compared with 15 to 20 percent of patients who did not receive this treatment. 

What is the current survival rate?

The current survival rate for oligometastatic cancer is, to some extent, dependent on the underlying cancer type that has developed oligometastasis. The prognosis from oligometastatic breast cancer, for example, is usually better than the prognosis from oligometastatic lung cancer - even though this is not always the rule. The rate depends on the underlying biology of the patient’s cancer and what are the available treatment options. 

In the SABR-COMET trial, again, there was a mixture of cancer types (breast, lung, colorectal, and prostate) that were treated with stereotactic radiotherapy to oligometastatic sites. In this trial, the five-year overall survival rate was only 18 percent for patients who just had continued drug treatments as would be standard for their cancer, whereas this number was significantly improved to 42.3 percent for patients who had stereotactic radiosurgery for their oligometastatic cancers. 

Dr Hiley is a highly esteemed consultant clinical oncologist who specialises in the stereotactic radiotherapy treatment for patients whose cancers have become oligometastatic. If you have recently developed oligometastatic cancer and you wish to seek the utmost quality clinical oncology care, don’t hesitate to visit Dr Hiley’s Top Doctors profile today.