Survival differences tied to right- versus left-sided colon cancers

Last Updated: 2016-11-04

By Joan Stephenson

NEW YORK (Reuters Health) - The location of a primary colon tumor on the colon's right or left side is associated with survival differences, and should be considered when establishing a prognosis and developing a treatment plan, according to a meta-analysis by Italian researchers.

As first author Dr. Fausto Petrelli of ASST Bergamo Ovest in Teviglio told Reuters Health by email, patients affected by left colon cancer have a 20% lower risk of death than do those with right colon cancer.

"Implications are enormous," he said, first for prognosis, and also for follow-up, stratification into clinical trials, and drug or surgical therapies.

The emergence of colon tumor location as a prognostic factor is supported by a growing body of evidence that the right and left colon have distinct biological properties that affect the tumors that develop in the two locations.

For example, the right and left colon have different embryological origins; differences in mucosal immunology, likely arising from differences in gut microbiota; and different molecular aberrations that can affect prognosis and may require different treatment approaches.

"This must be taken into consideration when we treat our patients or when we enroll them into clinical trials," Dr. Petrelli said.

He noted that recent randomized trials in patients with metastatic disease showed right colon cancers are usually less responsive than left colon tumors to anti-EGFR treatment, reflecting molecular differences in the tumors.

Dr. Petrelli and his colleagues conducted a systematic review and meta-analysis of prospective and retrospective studies of patients with stages 1-4 colon cancer that reported data on overall survival for left-sided primary tumors (excluding rectal cancers) compared with right-sided ones.

The analysis included 66 studies published from 1995 to 2016, involving more than 1.4 million patients with a median follow-up of 65 months.

Left-sided primary tumors were associated with a significantly reduced risk of death (hazard ratio, 0.82; p<0.001), the researchers report in JAMA Oncology, online October 27.

This difference was independent of stage, race, adjuvant chemotherapy, year of study, number of participants, and the quality of the studies.

The findings indicate that a primary colon tumor's location (left or right) should be recognized as a factor for establishing prognosis in both earlier and advanced stages of the disease, the researchers note.

"Moreover, primary tumor location should be carefully considered when deciding treatment intensity in metastatic and locoregional settings, and should represent an important stratification factor for future adjuvant studies," they write.

Right colon cancer likely needs "a more aggressive strategy in early and advanced disease," said Dr. Petrelli.

The finding that right-sided and left-sided colon cancers have different prognoses and also respond differently to targeted agents "will open up new ways to classify colorectal cancer patients and select more effective therapies for our patients," Dr. Heinz-Josef Lenz of the University of Southern California Norris Comprehensive Cancer Center, Los Angeles, told Reuters Health by email.

Tumor location should be included in clinical trial design as a stratifying factor, said Dr. Lenz, who was not involved in the study. Beyond that, he added, "the focus of translational and basic research is to study the molecular differences and develop more effective therapies for these two different colon cancers."

SOURCE: http://bit.ly/2e2ryVm

JAMA Oncol 2016.