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Tarlov E, Lee TA, Durazo-Arvizu R, Zhang Q, Bennett CL, Hynes DM. Adjuvant Chemotherapy in Colon Cancer: Differences by System of Care and Stage. Paper presented at: AcademyHealth Annual Research Meeting; 2009 Jun 28; Chicago, IL.
Research Objective: Practice guidelines for stage III colon cancer care include the routine use of chemotherapy following colectomy. Since clinical studies have failed to establish a definitive survival benefit of adjuvant chemotherapy in stage II, guidelines for that group have recommended that adjuvant chemotherapy be reserved for clinical trials or, more recently, be determined on a case-by-case basis in discussion between physician and patient. In the presence of uncertainty regarding most efficacious therapy, non-clinical factors such as practice environment or physician reimbursement incentives may emerge as influential determinants of treatment choice. In this study, we examined adjuvant chemotherapy use in stage II compared to stage III colon cancer in the Medicare fee-for-service system and in a prepaid and integrated healthcare system to ascertain the extent to which probability of receiving chemotherapy among patients with stage II cancer is influenced by system of care. Study Design: We conducted a retrospective cohort study of elderly veterans diagnosed with stage II or III colon cancer between 1999 and 2001 who had healthcare coverage through both the Department of Veterans Affairs (VA) and Medicare. Using linked cancer registry, VA, and Medicare data and Cox proportional hazards regression modeling, we examined the relationship between stage at diagnosis, system of care, and chemotherapy initiation. Population Studied: Veterans with colon cancer age 65 years and older who were dually eligible for VA and Medicare-funded healthcare. Principal Findings: We identified 1,005 veterans with stage II (59%) or III (41%) colon cancer who had undergone colectomy. Twenty percent were diagnosed in the VA and the remainder at non-VA facilities, 94% were male and mean age was 76 years. Twenty-eight percent of stage II and 62% of stage III patients received at least one chemotherapy treatment. The initial regression model controlled for stage and age at diagnosis, race, marital status, residential census tract income, comorbidities, year, and geographic region and revealed that compared to VA patients, non-VA patients were more likely to receive chemotherapy (IRR: 1.59, CI95%: 1.01 - 2.50). The addition of a stage-by-system interaction term to the model revealed that stage II patients outside the VA were over twice as likely as their VA counterparts to receive chemotherapy (IRR: 2.64, CI95%: 1.06 - 6.61) while patients with stage III cancer were equally likely to receive chemotherapy, irrespective of system of care (IRR comparing non-VA to VA patients: 1.23, CI95%: 0.88 - 1.70). Conclusions: The association between stage at diagnosis and receipt of chemotherapy depends on system of care; patients with stage II cancer who were diagnosed at non-VA facilities and whose care was covered by Medicare were much more likely to have adjuvant chemotherapy than patients treated in the VA. Among stage III patients, system of care had no impact on likelihood of adjuvant chemotherapy. Implications for Policy, Delivery or Practice: Further study is needed to uncover the drivers of these marked differences in use of a cancer treatment whose benefit has not been established. In view of high price tags on recently developed chemotherapy regimens, implications for costs of cancer care may be substantial.
