Duke 2008 | ASHE | Equity and Efficiency in Health and Healthcare

Objective: To estimate the cost attributable to colon cancer, treatment and survival in one year after diagnosis by cancer stage, and to estimate the differences in cost, treatment and survival between Medicare only and dually eligible beneficiaries

Data: We extracted an inception cohort of colon cancer patients aged 65 and older enrolled in Medicare Part A and Part B between 1997 and 2000 from the Michigan Tumor Registry. Medicare beneficiaries without cancer were matched to cancer patients by age, gender, race and residence of health service area. Statewide Medicare and Medicaid claims for inpatient, outpatient, physician office and hospice services were used to identify comorbid conditions and treatment regimens and to construct total costs 1 year before and after cancer diagnosis. Oneyear survival was ascertained through the Medicare denominator file and National Death Index.

Methods: We used the difference-in-differences method to estimate costs attributable to cancer, controlling for costs prior to cancer diagnosis. Because a substantial proportion of patients had zero cost in the 12 months prior to diagnosis and control patients had zero cost in both periods, two-part models were estimated. In the second part of the two-part models, we systematically compared log-, Boxcox-, square root transformation and generalized linear model with gamma distribution through a series of tests for distribution, nonlinearity, goodness of fit, and overfitting for the overall model and for each part separately. The best fitted models were used to estimate mean total cancer cost in 1 year.

Results: The mean total cost attributable to colon cancer one year after diagnosis was $22,609. Patients diagnosed with in situ and local stage had the lowest costs ($18k), followed by patients with distant or unknown stage ($24k), and patients with regional cancer had the highest cost ($26k). Given the same stage of diagnosis, those with more comorbid conditions had higher costs but the relationship between cost and age was nonlinear where cost first increased and then decreased by age but peaked at different age group for different stage of cancer. Overall treatment costs did not differ between Medicare and the dually eligible patients. However, dually eligible patients with distant stage cancer consistently had significantly lower costs than their Medicare counterparts despite similar survival times and treatments received in this group. There was a clear survival benefit associated with resection combined with chemotherapy for all stages of disease. Controlling for age, race, sex and comorbid conditions, the dually eligible patients had worse survival than the Medicare only patients overall and among early stages of cancer.

Conclusions: Our assessment of colon cancer costs offers several insights. First, the method used is a viable alternative to methods that segment the cancer treatment experience into phases. Second, cancer treatment cost varies by stage of diagnosis, age, and comorbid conditions and suggests that early stage cancer, which is likely to increase given recent screening initiatives, results in lower cancer costs relative to more advanced stages. Finally, with similar treatment cost dually eligible patients with early stages of cancer experience survival and treatment disparities relative to Medicare patients. Further investigation into the cause of this inefficiency is warranted.