STAGE, AGE, COMORBIDITY, AND DIRECT COSTS OF COLON, PROSTATE, AND BREAST-CANCER CARE

Purpose: This study was conducted to evaluate the effect of stage at d iagnosis, age, and level of comorbidity (presence of other illness) on the costs of treating three types of cancer among members of a health maintenance organization. Methods: Among 388 000 members enrolled any time during 1990 and 1991 in Group Health Cooperative (GHC) of Puget S ound (Washington State), we estimated the total and net direct costs o f medical care for colon, prostate, and breast cancers, including both incident (290, 554, and 645 patients, respectively) and prevalent (10 46, 1295, and 2299 patients, respectively) cases. We summarized costs for initial, continuing, and terminal phases of care. Net costs were t he difference between the costs of the care of each case subject and t he average costs of the care for all enrollees without the cancer of i nterest who were of the same sex and in the same S-year age group. Dif ferences in estimated total and net costs by stage at diagnosis, age, and comorbidity were separately evaluated using multivariate regressio n modeling. All P values were two-sided. Comorbidity was based on a sc ore calculated from 1988 pharmacy data. Results: Total costs of initia l care increased with stage at diagnosis for colon (P = .0013) and bre ast (P<.0001) cancer cases, but not for prostate cancer cases. Total i nitial costs decreased with age for prostate (P = .0225) and breast (P = .0002) cancers but did not change with degree of comorbidity for an y of the three cancers. Total continuing medical care costs increased with stage at diagnosis for colon (P<.0001) and breast (P<.0001) cance r cases but not for prostate cancer cases. Total terminal care costs w ere similar by stage for all three cancers. Net initial costs differed with stage for all three cancers (P<.05). Net continuing care costs i ncreased with stage (P<.0001) and decreased with age (P<.001) for colo n and breast cancers but not for prostate cancer. Net continuing care costs decreased with comorbidity for all three cancers (P = .004, P = .011, and P<.0001 for colon, prostate, and breast cancers, respectivel y). Among regional stage cancers, continuing care costs decreased with age for colon (P<.0017) and breast (P = .033) cancers but not for pro state cancers. Conclusions: The results show that total costs vary by stage at diagnosis and age, but the patterns of variation differ for e ach cancer. Costs of cancer are not simply additive to costs of other conditions. Implications: More needs to be done to explore the reasons and implications of age-related cost differences. Cost-effectiveness analyses of cancer control interventions that shift cancer stage distr ibutions may need to consider both the age and comorbidity of the targ et populations.