Study: Multiple sclerosis may affect breast and colorectal cancer survival

IN-DEPTH REVIEW OF RESEARCH

Study background

People living with MS have a lower life expectancy than those without MS. Among people with MS, cancer has been reported as the second or third most common cause of death in adults with MS, after death due to MS-related causes. Among people living with MS, cervical, breast and colon cancers are the most diagnosed cancers.

Little is known about outcomes after a breast or colon cancer diagnosis in people living with MS. Few studies have focused specifically on survival after a cancer diagnosis in people with MS and research has shown conflicting results.

Some studies have suggested that there is similar or better overall survival among people with MS after a breast cancer diagnosis. In two small Swedish studies, survival after a breast cancer diagnosis was the same in people without MS. Another study observed that women with MS had better overall survival than those without MS.

Only one study has looked at survival in patients with MS after a diagnosis of colon cancer. In this small Swedish study, people with MS had better overall survival than people without MS. Another Swedish study showed that overall survival was higher in patients with MS who were diagnosed with any gastrointestinal cancer compared to people without MS who had a gastrointestinal  cancer diagnosis. Cancer-specific survival and overall survival specifically after a colon cancer diagnosis was not reported.

Researchers of these studies wanted to know

The Canadian research group conducted two similarly designed studies. One looked at whether overall and cancer-specific survival after a breast cancer diagnosis was lower in people with MS compared to people without MS. The other looked at whether overall and cancer-specific survival in people diagnosed with colon cancer was lower in people with MS compared to people without MS.

Populations looked at in the breast cancer study

The breast cancer study included 779 patients with MS and 3,116 controls (patients without MS). All participants had been diagnosed with breast cancer, most with early-stage disease (stages I or II). The mean age at diagnosis was 58 years.

The study was done in Canada with participants from two Canadian provinces—Ontario (which had more urban residents and almost 40 percent of the country’s population) or Manitoba (which has more rural residents).

Study design

This was a matched cohort study. Four participants without MS were matched to each person based on their birth year, year of cancer diagnosis and province.

Study findings

• People with MS and breast cancer had a 28% lower overall survival compared to those with breast cancer and without MS.
  • The reason for this difference is unknown. Possible reasons may include disability in women with MS. For example, women with more MS-related disabilities may face barriers to treatment, have received less aggressive treatment or be more susceptible to complications from treatment or other factors that decreased overall survival. Another possibility is that breast cancer or treatment for breast cancer worsened MS.
• MS did not alter breast cancer-specific survival.

Populations looked at in the colon cancer study

The colon cancer study included 338 patients with MS and 1,352 controls (patients without MS). All participants had been diagnosed with colon cancer. The median age at diagnosis was 65 years.

The study was done in Canada with participants from two Canadian provinces—Ontario (which has more urban residents and almost 40 percent of the country’s population) or Manitoba (which has more rural residents).

Study design

This was a matched cohort study. Four participants without MS were matched to each participant with MS based on birth year, year of cancer diagnosis and province.

Study findings

• People with MS and colon cancer had a 41% lower overall survival compared to those with colon cancer without MS.
  • This was highest in the first 6 to 12 months after colon cancer diagnosis (45% decrease) and decreased with time at 1, 2 and 5 years after diagnosis.
    • The reasons for lower overall survival in people with MS are unknown. Possible reasons may include barriers to care, stage and/or age at diagnosis or that people with MS do not tolerate colon cancer treatment (surgery, chemotherapy) as well as people without MS.

• MS was linked with a 27% greater chance of dying of colon cancer, specifically in the 6-month period after diagnosis. This effect was not seen at other times after cancer diagnosis.

Strengths and limitations

The same group of researchers conducted both studies. The study designs were identical.

Strengths

• The design of the studies was a strength. Cancer patients without MS were matched to cancer patients with MS by birth year, year of cancer diagnosis and where they lived. Four patients without MS were matched to each patient with MS. This ratio (4 matched patients without MS for each patient with MS) strengthened results.
• Unlike other studies, these two studies looked at both overall and cancer-specific survival.
• The studies were done in Canada, a country with universal health care. This likely resulted in most patients being treated similarly.

Limitations

• The data analyzed did not have information on race or ethnicity, factors that are known to be associated with breast and colon cancer outcomes. It is not known whether the impact of MS on cancer survival would be different in people of different racial or ethnic groups.
• The researchers could not assess how drug therapies for MS might impact overall or cancer-specific outcomes, as Ontario lacks population-based prescription data for people under 65.
• On death certificates, the cause of death due to cancer did not show the type of cancer. The primary site of the cancer was not reported. Therefore, researchers may have underestimated the number of deaths that were specifically due to breast or colon cancer.
• The study did not include information about genetic testing results. It is not known whether the impact of MS on survival would be different in people with inherited mutations.

Context

Studies have shown no difference in the risk of breast or colon cancer in people with MS compared to people without MS. The few studies that have looked at survival after a breast or colon cancer diagnosis in people with MS reported conflicting results. Some suggested better overall survival following a breast cancer diagnosis and no difference in cancer-specific survival. A small study reported that overall survival after a diagnosis of cancer in the upper and lower gastrointestinal tracts (gut) was higher in patients with MS compared to patients without MS. These studies contrast with other studies that suggest people with serious chronic illnesses such as diabetes or psychiatric disorders have reduced overall survival after a cancer diagnosis. The two studies reviewed here suggest that like other chronic illnesses, MS may reduce overall survival after a cancer diagnosis.

Conclusions

A better understanding of how breast and colon cancer treatment decisions and the types and duration of treatments impact outcomes for people living with MS is needed. Additional research will provide a better understanding of the factors that worsen outcomes. Knowing these factors will give patients and their healthcare providers important information to guide cancer treatments and improve outcomes and quality of life for people with MS who are diagnosed with breast or colon cancer.

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posted 12/10/21