Tumor biology in older breast cancer patients--what is the impact on survival stratified for guideline adherence? A retrospective multi-centre cohort study of 5378 patients.

Purpose: The tumor biology of older breast cancer patients (oBCP) is usually less aggressive, however applied adjuvant treatment is often less potent resulting in an impaired disease free survival and overall survival in this group. This study tries to answer the following questions for the biological subtypes of oBCP (70+ y):
Methods: Between 1992 and 2008 the BRENDA ('BRENDA' = quality of BREast caNcer care unDer evidence-bAsed guidelines) study group recorded medical data of 17 participating certified breast cancer centers in Germany. We performed a retrospective multi-center database analysis of 5632 patient records. Guideline-adherent-treatment (GL+) of oBCP(n = 1918) was compared to GL+ of yBCP(n = 3714).
Results: OBCP were more likely to have hormone receptor positive (HR+) and HER2neu negative (HER2-) breast cancer (77.5% vs 74.5%). The rate of GL- was significantly different (p < 0.001) between the age groups and the biological subgroups (yBCP vs oBCP: 21.8%vs38.8% (HR+/HER2-); 30.6%vs49.7% (HR+/HER2+); 23.6%vs69.5% (HR-/HER2+); 31.4%vs67.8% (TNBC)). The survival parameters for HR+/HER2- and TNBC were significantly worse in case of GL- regarding chemotherapy, and if applicable endocrine therapy. A similar association only existed in HR-/HER2+ tumors for GL- for radiotherapy and in HR+/HER2+ tumors for chemotherapy.
Conclusions: Beside the significantly different distribution of biological subtypes in the age groups there is an association between biological subtype, and GL+ influencing survival parameters in oBCP.
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