We identified 4,388 patients diagnosed with stage II or III CRC who received chemotherapy and met all eligibility criteria for inclusion (). The study population was primarily over the age of 70 at diagnosis (73%), White Non-Hispanic (81%), married (61%), living in a metropolitan area (84%), and free from comorbidities (68%). Most tumors were located in the colon (85%) and diagnosed at stage III (74%) ().
Characteristics of older stage II or III colorectal cancer patients by chemotherapy treatment group*
The majority of the 1,517 physicians were male (81%), MDs (97%), US-trained (67%), medical school graduates ≥1981 (56%) with a primary specialty of oncology or hematology/oncology (76%) (). Three percent of the 773 hospitals had a NCI clinical or comprehensive cancer center designation and 48% had at least one cooperative group membership. Almost 40% were teaching hospitals and 62% were non-profit entities.
Characteristics of physicians and hospitals providing care for older stage II and III colorectal cancer patients
The prevalence of adjuvant oxaliplatin treatment over the 4-year study period was 52% and 46% for patients diagnosed with colon and rectal cancer, respectively. There was a steady increase in the prevalence of adjuvant oxaliplatin use over time which was similar for all site and stage subgroups (). By 2007, 60% and 73% of stage II and III colon and 52% and 68% of stage II and III rectal cancer patients received oxaliplatin, respectively.
Prevalence of adjuvant oxaliplatin use by cancer site and stage among older colorectal cancer patients who received chemotherapy treatment from 2004–2007
Patients diagnosed in earlier years were less likely to receive adjuvant oxaliplatin than those diagnosed in 2007 (e.g., 2004: aPR=0.42, 95% CI: (0.37, 0.47), ). Patients with colon vs. rectal cancer were more likely to receive oxaliplatin (aPR=1.15, 95% CI: (1.05, 1.26)), whereas those with stage II vs. III disease were less likely (aPR= 0.65, 95% CI: (0.60, 0.71)). Increasing age was associated with a gradual monotonic decrease in the likelihood of oxaliplatin receipt (e.g., 85+ vs. 66–69: aPR =0.22, 95% CI: (0.14, 0.34)) and patients with increased comorbidities were less likely to receive oxaliplatin compared to those with no comorbidity (e.g., Charlson Score of 1 vs. 0: aPR= 0.92, 95% CI: (0.87, 0.98). Additionally, patients who were separated, divorced or widowed (vs. married), living in the East or Midwest (vs. West), residing in a non-metropolitan area (vs. metropolitan area) or in a census tract with a higher proportion of individuals living under the poverty level were less likely to receive oxaliplatin. No physician- or hospital-level variables were strongly associated with adjuvant oxaliplatin receipt in the overall analysis. Results from the cancer site-stratified analyses were similar, although less precise for rectal cancer due the smaller number of patients (data not shown). Two exceptions were that among rectal cancer patients, surgical treatment at an NCI comprehensive cancer center was associated with increased adjuvant oxaliplatin use (aPR=1.48, 95% CI: 1.15, 1.90), while Hispanic ethnicity was associated with decreased use (aPR=0.52, 0.32, 0.86). Among stage II colon cancer patients, more patients with T4 tumors (40%) received oxaliplatin compared to those with T3 tumors (36%).
Forest plot summarizing the multivariable adjusted prevalence ratio estimates for the associations between multilevel characteristics and adjuvant oxaliplatin receipt among older stage II and III CRC patients treated with chemotherapy
The category headings in denote the AUC for components of the logistic regression model (calendar year, patient/tumor, physician, hospital, and geographic). The AUC reports the ability of each model to accurately distinguish between those patients who received adjuvant oxaliplatin and those who did not. When calendar year was included alone, the model had fair ability to discriminate oxaliplatin users (AUC=68%). The addition of patient/tumor factors enhanced the model’s discriminatory ability (AUC=75.8 %). However, when physician, hospital, and geographic factors were added separately to calendar year, the AUC only increased to 68.9%, 68.9%, and 69.1% respectively. The full model AUC was 76.6%; therefore, among patients who received chemotherapy, physician and hospital characteristics contributed very little to the determination of oxaliplatin receipt.