Subgroups of cognitively affected and unaffected breast cancer survivors after chemotherapy: a data-driven approach

Abstract

Purpose: It is assumed that a segment of breast cancer survivors are cognitively affected after chemotherapy. Our aim is to discover whether there is a qualitatively different cognitively affected subgroup of breast cancer survivors, or whether there are only quantitative differences between survivors in cognitive functioning.

Methods: Latent profile analysis was applied to age-corrected neuropsychological data -measuring verbal memory, attention, speed, and executive functioning- from an existing sample of 62 breast cancer survivors treated with chemotherapy. Other clustering methods were applied as sensitivity analyses. Subgroup distinctness was established with posterior mean assignment probability and silhouette width. Simulations were used to calculate subgroup stability, posterior predictive checks to establish absolute fit of the subgrouping model. Subgrouping results were compared to traditional normative comparisons results.

Results: Two subgroups were discovered. One had cognitive normal scores, the other -45%- had lower scores. Subgrouping results were consistent across clustering methods. The subgroups showed some overlap; 6% of survivors could fall in either. Subgroups were stable and described the data well. Results of the subgroup clustering model matched those of a traditional normative comparison method requiring small deviations on two cognitive domains.

Conclusions: We discovered that almost half of breast cancer survivors after chemotherapy form a cognitively affected subgroup, using a data-driven approach. This proportion is higher than previous studies using prespecified cutoffs observed.

Implications for cancer survivors: A larger group of cancer survivors may be cognitively affected than previously recognized, and a less strict threshold for cognitive problems may be needed in this population.

Keywords: Breast cancer; Chemotherapy; Cognitive impairment; Executive functioning; Subgroups; Verbal memory.