Molecular effects of ovarian stimulation for fertility preservation in breast cancer: a paired-biopsy analysis.

BACKGROUND

Fertility preservation is increasingly offered to young women diagnosed with breast cancer. Although available clinical evidence suggests that controlled ovarian stimulation (COS) does not compromise oncological outcomes, its direct biological effect on tumor tissue remains poorly defined.

PATIENTS AND

METHODS

In this single-center, longitudinal, prospective paired-biopsy study, 21 premenopausal women (age <40 years) with stage II-III breast cancer underwent paired diagnostic and post-COS tumor biopsies at the Breast Cancer Unit, Clínic BCCC (October 2020-September 2024). COS was carried out with recombinant follicle-stimulating hormone plus concurrent letrozole (5 mg/day) using a random-start protocol. After oocyte retrieval, a second core tumor biopsy was obtained within 24 to 48 hours. Immunohistochemistry [estrogen receptor (ER), progesterone receptor (PR), Ki-67, human epidermal growth factor receptor 2 (HER2,) tumor-infiltrating lymphocytes (TILs)] and PAM50 gene-expression profiling were carried out. Paired analyses evaluated changes in protein markers, gene-by-gene expression, intrinsic subtype, and risk of recurrence (ROR) score, applying a false discovery rate (FDR) <5% for significance.

RESULTS

No significant differences were detected in ER (P = 0.962), PR (P = 0.562), Ki-67 (P = 0.768), or TILs (P = 0.172) after COS. Post-stimulation Ki-67 was not associated with stimulation duration (r = 0.047; P = 0.839), total gonadotropin dose (r = 0.026; P = 0.911), or peak estradiol levels (r = 0.121; P = 0.610). Transcriptomic analysis identified downregulation of 11/72 genes (15.3%), including proliferation-associated genes CDC6, CENPF, EXO1, and RRM2, although none met significance thresholds after FDR correction. PAM50 intrinsic subtype remained stable (luminal A 23.8%, luminal B 28.6%, HER2-enriched 19.0%, basal-like 23.8%), with only two borderline shifts between luminal A and luminal B. Five mild ROR variations were observed (four decreases and one increase), all small in magnitude on the continuous scale.

CONCLUSIONS

COS with concurrent letrozole was not associated with short-term molecular changes in breast tumor tissue. These findings provide biological reassurance regarding the safety of COS for fertility preservation in young women with breast cancer.