Despite the powerful evidence that chemotherapy after surgery for Stage III colon cancer can improve survival, results of this study confirm previous studies that suggested that some groups of patients do not receive standard of care for this disease. Similar to other studies, age, marital status and comorbidity were major predictors of receipt of chemotherapy.11
For some individuals, adjuvant chemotherapy may not have been given due to contraindications from concurrent medical conditions. Our survival model suggested that adjuvant chemotherapy was protective among patients with and without comorbidities, and therefore seemed to suggest that, at least for some patients with higher comorbid illness burdens, adjuvant treatment can be protective. However, we did not have detailed information about severity of comorbid conditions within the categories used in our analysis to examine this further.
Geographic differences by state persisted after adjustment for other factors, and have not been studied as extensively. Interstate differences in receipt of treatment are likely a result of local practice patterns, lack of uniform acceptance of this treatment, and lack of access to treatment facilities. Regional differences in receipt of treatment also were seen in an earlier California study,11
as well as variation by hospital. In a survey of physicians, the most common reasons cited for not providing adjuvant chemotherapy for Stage III colon cancer were patient refusal, comorbid illness, and lack of clinical indication.11
Despite NIH recommendations, over 20% of physicians reported that adjuvant chemotherapy was not clinically indicated for their Stage III colon cancer patients.11
Interestingly, interstate differences in receipt of chemotherapy did not appear to correlate with interstate differences in survival, and it is likely that other factors are involved. This may be attributable in part to differences by state in the number of cases excluded from the survival analysis. Survival after diagnosis for patients in this study was influenced by age, comorbid illness, and receipt of chemotherapy.
Receipt of adjuvant treatment for patients in NPCR states appeared to be slightly, although not substantially, lower than for patients in areas covered by the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) program. Results from SEER Patterns of Care studies reported that use of adjuvant chemotherapy for Stage III colon cancer increased between 1989 and 1990 when the NIH consensus conference was held, and has remained relatively stable since 1990.12
Receipt of chemotherapy in 1995 by patients with Stage III colon cancer in the SEER study was 90% for patients aged 55 or younger. This is slightly higher than the 86% of patients aged 50 or younger in the current study diagnosed in 1997. There is some evidence that patients residing in SEER areas are somewhat more affluent than other areas of the U.S,13
and they may have greater access to high quality cancer care. Receipt of treatment for older patients in the current study was comparable to that for similarly aged patients studied using linked SEER-Medicare data. Treatment rates for patients diagnosed with Stage III colon cancer between 1991 and 1996 and identified through the SEER program were 78% for those aged 65 to 69, and 74% for those aged 70–74, similar to the 75% for patients aged 65–74 in the current study diagnosed in 1997.14
Patients residing in neighborhoods with less education were less likely to have received adjuvant chemotherapy, although residence in poor neighborhoods did not have a statistically significant effect after adjustment for other factors. Patients residing in rural areas of the U.S. were not substantially less likely to have received treatment. Adjuvant chemotherapy is usually administered in outpatient treatment facilities and does not require the access to specialized treatment facilities required by adjuvant radiation treatment. Type of health insurance did not have a significant effect on receipt of treatment after adjustment for other factors, and did not influence survival. The majority of patients in the analysis were aged 65 or older and would have been covered by Medicare.
Our study was subject to several limitations. First, data were collected from seven states and are therefore not necessarily generalizable to all states. Moreover, data for this study were collected five years after the cancer diagnosis year, and therefore some patient records were not retrievable. Additionally, completeness of chemotherapy data may vary by registry. Our measures of socioeconomic status were derived from Census data and were therefore not individual-level data. Furthermore, we only collected comorbidities that had been coded on the face sheets of patients’ medical records. Therefore, comorbidities may have been underreported. Finally, we were unable to examine cause-specific mortality in addition to overall mortality.
The CDC-NPCR Patterns of Care study follows the National Cancer Policy Board recommendation that data systems such as the NPCR be used to conduct surveillance of cancer treatment in the United States. The study demonstrated the need for surveillance of cancer treatment across the U.S. by confirming gaps in treatment for some groups. This study also documented the substantial challenges to treatment surveillance using cancer registry treatment data. Analysis of quality of registry treatment data for patients in this study showed that only about 71% of chemotherapy received by colon cancer patients was captured by cancer registries through routine data collection.6
Use of registries for treatment surveillance will continue to require that treatment contained in the NPCR registries, as in SEER registries, be supplemented with data collection in physician offices and other treatment facilities.