To consider the question of when to prescribe adjuvant treatment for elderly breast cancer patients, particularly when comorbidities are present. Knowledge of the threshold relapse risks above which adjuvant treatment is worth prescribing would enhance decision making.

A Markov analysis of data from the medical literature was conducted. Patients aged 65 to 85 years were considered, along with three levels of comorbidity. The threshold risk of relapse at 10 years (RR10), at which time treatment provides absolute reduction or reduction of an absolute 1% in relapse or mortality, was evaluated.

The threshold RR10 for an absolute reduction in mortality risk by adjuvant treatment was low through the age of 85 years. However, for an absolute 1% reduction, the effect of treatment on relapse and the effect of treatment on mortality increasingly diverged. The threshold RR10 for an absolute 1% reduction in relapse risk remained fairly low (5% to 6% for tamoxifen, 12% to 19% for chemotherapy). The threshold RR10 for an absolute 1% reduction in mortality risk, although starting close to the RR10 for an absolute 1% reduction in relapse risk, rose sharply. For tamoxifen, the difference between the two was 4% for an average 65-year-old, 6% at the age of 75 years, and 15% at the age of 85 years. For chemotherapy, the differences were 6%, 12%, and 30%, respectively. Similarly, thresholds increased with increasing comorbidity. In older and sicker patients, the maximum benefit was reached after 5 years rather than 10 years.

Older breast cancer patients can expect a reduction in relapse that is fairly similar to that of younger patients. However, the effect on mortality diverges markedly, and attention should be paid to this difference in clinical decision making. Comorbidity should be considered in recommendations for adjuvant treatment, including clinical practice guidelines.