Background : Due to inherent anatomical differences between adult natal male and female chests, the traditional Tanner sexual maturity rating scale does not adequately capture the breast changes that occur in trans-female patients taking cross sex hormone therapy. Moreover, there is a paucity of literature examining patient and treatment factors that influence breast development in this population. We have developed a novel breast development scale for trans-females that accounts for these inherent differences and also includes physical attributes known to contribute to aesthetically pleasing breasts.
Methods : The Breast Response to Estrogenic Stimulation in Transgender women (BREST) scale was developed and used to categorize 99 trans-female breast development with multiple photographic views of the right and left breast. Two plastic surgery residents and a plastic surgery faculty member graded all 99 patients to allow for inter-rater reliability calculation. Demographic data including age, race, type and duration of hormone therapy, pre-operative breast dimensions, and surgical characteristics were collected for statistical analysis.
Results : The BREST Scale exhibited moderate inter-rater reliability (Kappa=0.58). Using a multivariate ordinal logistic regression model, the BREST scale was found to be associated with duration of hormone therapy, pre-operative bust-chest circumference difference, inter-nipple distance and nipple-to-inframammary fold distance. Patients in BREST categories I-IV received sub-muscular dual-plane III implant placement while patients in BREST category V received sub-glandular implant placement.
Conclusions : The BREST scale exhibits moderate inter-rater reliability, but is strongly associated with objective pre-operative breast measurements. More importantly, the BREST scale provides a transgender-specific framework to better evaluate breast growth in response to cross-sex hormone therapy. Prospective studies using the BREST scale may further elucidate which patient and treatment factors produce the most aesthetically pleasing breast. Additional patient-reported studies will also be needed to correlate the BREST scale with what transgender patients feel are the most aesthetic breast qualities.