The findings contradict two recent reports of higher mortality with right-sided colon cancers -- one of which drew from the same national database but controlled for different factors.
The new study used a more limited sample of patients and controlled for more factors, including personal and socioeconomic demographics, treatment variables, and disease-related features such as tumor size and stage, presentation (urgent or not), lymph node involvement, and year of diagnosis (before or after Medicare started paying for colonoscopies).
Dr. Jennifer Weiss at the University of Wisconsin and colleagues used the Surveillance, Epidemiology, and End Results (SEER) registry to identify nearly 54,000 patients, age 66 and older, who were diagnosed with stages I to III colon adenocarcinoma between 1992 and 2005.
In unadjusted analyses, right-sided cancers predicted worse five-year mortality in all patients except those diagnosed at stage II, the authors reported online October 3 in the Journal of Clinical Oncology.
Multivariate analysis, however, showed no significant overall difference in five-year mortality between patients with right- and left-sided cancers.
In the adjusted model as well, however, stage II right-side cancers were associated with lower mortality than similarly staged left-sided cancers (hazard ratio = 0.92, p = 0.001).
The results "highlight that the relationship between mortality and tumor location in colon cancer is not straightforward" and is instead "stage dependent," Dr. Weiss and her associates wrote.
They believe that microsatellite instability (MSI) -- a favorable marker seen more commonly in right-sided colon cancers -- may account for the difference. The SEER database does not include MSI tumor status, however, and the investigators couldn't test the hypothesis in this study.
If the findings are confirmed, they may impact the use of adjuvant chemotherapy in patients with stage II colon cancers, the investigators said.
J Clin Oncol 2011.
Last Updated: 2011-11-03 19:01:09 -0400 (Reuters Health)
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