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LAS VEGAS -- A history of endometrial cancer at a younger age quadrupled the likelihood of a subsequent diagnosis of colorectal cancer, a retrospective analysis of administrative data showed.

That increased risk of colorectal cancer pertained to women who were 50 or younger at diagnosis of endometrial cancer. Limiting the analysis to right-sided colorectal cancer, the investigators found an increased risk that extended to women who were up to 65 at the time of endometrial cancer diagnosis.

"Colorectal cancer screening with colonoscopy should be considered soon after diagnosis of endometrial cancer for all women," Harminder Singh, MD, of the University of Manitoba in Winnipeg, said here at the American College of Gastroenterology meeting.

The findings came from an investigation that had its origin in a combination of observations that provided a circumstantial link between endometrial cancer and colorectal cancer.

As Singh pointed out, endometrial cancer is the most common cancer affecting a woman's reproductive system. A higher proportion of colorectal cancers in women are right sided, possibly because of a hormonal effect, which might be exaggerated in women who have a history of endometrial cancer.

No previous studies have provided data on the site-specific incidence of colorectal cancer occurring after endometrial cancer, Singh continued. Moreover, previous studies of colorectal cancer in endometrial cancer survivors did not account for competing risks, such as higher rates of other types of cancer.

To examine in greater detail the relationship between endometrial and colorectal cancers, Singh and colleagues searched the Manitoba Cancer Registry and several additional databases maintained by Manitoba Health, the provincial health system. They identified all new diagnoses of endometrial cancer from April 1987 through December 2008. Patients registered with Manitoba Health for less than 3 years and those with a history of cancer were excluded.

Each patient with endometrial cancer was matched with five women who did not have endometrial cancer.

Follow-up continued through Dec. 31, 2009.

The investigators tracked competing and mutually exclusive outcomes, including diagnosis of colorectal cancer, diagnosis of other cancers, and death. Their analyses were adjusted for potential confounders that included age at diagnosis of colorectal cancer, diabetes, lower gastrointestinal endoscopy, and socioeconomic status.

They performed analyses stratified by time since diagnosis of endometrial cancer, age at diagnosis of endometrial cancer, and outcome by site of colorectal cancer.

The overall analysis included 3,115 women with endometrial cancer and a matched control group of 15,084 women who did not have endometrial cancer. The study population had a cumulative follow-up of 145,502 person-years.

The time interval since diagnosis of endometrial cancer had no effect on the risk of developing colorectal cancer.

Age at diagnosis of endometrial cancer had a significant influence on the subsequent risk of colorectal cancer -- diagnosis at age 50 or younger was associated with a hazard ratio of 4.41 for colorectal cancer (95% CI 1.47 to 13.26); diagnosis of endometrial cancer after 50 did not affect the hazard for colorectal cancer.

An analysis limited to right-sided colorectal cancer yielded significant associations with the time interval since diagnosis of endometrial cancer. Overall, a history of endometrial cancer almost doubled the hazard for right-sided colorectal cancer (HR 1.93, 95% CI 1.25 to 3.00).

Among women more than 5 years removed from diagnosis of endometrial cancer, the hazard for colorectal cancer tripled (HR 2.99, 95% CI 1.60 to 5.60).

The risk of right-sided colorectal cancer increased more than sevenfold among women whose endometrial diagnosis occurred at age 50 or younger (HR 7.48, 95% CI 1.29 to 43.28) and was more than doubled in women 51 to 65 at diagnosis of endometrial cancer.

An endometrial cancer diagnosis after age 65 did not significantly affect the risk of right-sided colorectal cancer.

Sensitivity analysis showed that effect size was not significantly changed when the definition of right-sided colorectal cancer included cancer in and proximal to the splenic flexure.

Endometrial cancer diagnosed after 1995 (versus earlier) also did not change the effect size, nor did use of hormone replacement therapy or nonsteroidal anti-inflammatory drugs.

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