RESUMEN
Over recent years, adjuvant systemic treatment guidelines (AST) for early-stage breast cancer have changed considerably. We aimed to assess the impact of these guideline changes on the administration of AST in early-stage breast cancer patients and to what extent these guidelines are adhered to at a nation-wide level. We used Netherlands Cancer Registry data to describe trends in AST prescription, adherence to AST guidelines, and to identify clinicopathological determinants of nonadherence. Between 1990 and 2012, 231,648 Dutch patients were diagnosed with early breast cancer, of whom 124,472 received AST. Adjuvant endocrine treatment (ET) use increased from 23 % of patients (1990) to 56 % (2012), and chemotherapy from 11 to 44 %. In 2009-2012, 8 % of patients received ET and 3 % received chemotherapy without guideline indication. Conversely, 10-29 % of patients did not receive ET and chemotherapy, respectively, despite a guideline indication. Unfavorable clinicopathological characteristics generally decreased the chance of undertreatment and increased the chance for overtreatment. Remarkable was the increased chance of ET undertreatment in younger women (RR < 35 vs 60-69 years 1.79; 95 % CI 1.30-2.47) and in women with HER2+ disease (RR 1.64; 95 % CI 1.46-1.85). Over the years, AST guidelines expanded resulting in much more Dutch early breast cancer patients receiving AST. In the majority of cases, AST administration was guideline concordant, but the high frequency of chemotherapy undertreatment in some subgroups suggests limited AST guideline support in these patients.