Patterns of Referral for Adjuvant Chemotherapy for Stage II and III Colon Cancer: A Population-Based Study

Reasons for variable utilization of adjuvant chemotherapy (ACT) for colon cancer have not been well described. We report medical oncology (MO) referral patterns and subsequent use of ACT.

Treatment records were linked to the population-based Ontario Cancer Registry to describe MO referral and ACT use among 5289 patients with stage II-III colon cancer treated in 2002-2008. Modified Poisson regression was used to analyze factors associated with MO referral and ACT use. Multilevel modeling was used to explore the proportion of variation in practice attributable to providers.

There was wide geographic variation in MO referral rates for stage II (range 37-80 %, p < 0.001) and stage III disease (range 77-98 %, p < 0.001). Use of ACT among referred patients varied across regions for stage II (range 12-49 %, p < 0.001) but not stage III (range 67-79 %, p = 0.353). For both stages, younger patients (p < 0.001) with less comorbidity (p < 0.010) were more likely to be referred to MO and treated with ACT. Applying the fitted regression model to nonreferred stage III patients suggests that 38 % had >50 % probability of having ACT if they had seen a MO. Among stage III patients, 15 % percent of the variance in MO referral rate and 6 % of the variance in ACT utilization rate is attributable to the surgeon and MO respectively.

A substantial proportion of non-referred patients with stage III colon cancer may have been offered ACT if they had seen MO. A small proportion of variance in referral rate and ACT treatment is attributable to providers.