“Incidence of invasive breast cancer in women treated with testosterone implants: a prospective 10-year cohort study” (Glaser, York, Dimitrakakis, 2019) reports outcomes from a prospective 10-year cohort of pre- and postmenopausal women treated with subcutaneous testosterone implants (with some receiving testosterone combined with anastrozole). The study was specifically designed to examine whether long-term implant therapy was associated with changes in invasive breast cancer incidence, using age-matched SEER rates and historical comparisons as reference points.

In short: this paper is often cited because it evaluates breast cancer incidence over a long horizon in women receiving testosterone implants, and reports no increase in invasive breast cancer incidence compared with age-matched expectations.