Estradiol [AP]

HER2 transactivation by the HER3 ligand heregulin (HRG) promotes an endocrine-resistant phenotype in the estrogen receptor-positive (ER+) luminal-B subtype of breast cancer. The underlying biological mechanisms that link them are, however, incompletely understood. Here, we evaluated the putative role of the lipogenic enzyme fatty acid synthase (FASN) as a major cause of HRG-driven endocrine resistance in ER+/HER2-negative breast cancer cells. MCF-7 cells engineered to stably overexpress HRG (MCF-7/HRG), an in vitro model of tamoxifen/fulvestrant-resistant luminal B-like breast cancer, showed a pronounced up-regulation of FASN gene/FASN protein expression. Autocrine HRG up-regulated FASN expression via HER2 transactivation and downstream activation of PI-3K/AKT and MAPK-ERK1/2 signaling pathways. The HRG-driven FASN-overexpressing phenotype was fully prevented in MCF-7 cells expressing a structural deletion mutant of HRG that is sequestered in a cellular compartment and lacks the ability to promote endocrine-resistance in an autocrine manner. Pharmacological inhibition of FASN activity blocked the estradiol-independent and tamoxifen/fulvestrant-refractory ability of MCF-7/HRG cells to anchorage-independently grow in soft-agar. In vivo treatment with a FASN inhibitor restored the anti-tumor activity of tamoxifen and fulvestrant against fast-growing, hormone-resistant MCF-7/HRG xenograft tumors in mice. Overall, these findings implicate FASN as a key enabler for endocrine resistance in HRG+/HER2- breast cancer and highlight the therapeutic potential of FASN inhibitors for the treatment of endocrine therapy-resistant luminal-B breast cancer.

Purpose Leydig-cell tumours (LCT) of the testis are poorly understood clinically. The aim of this report is to analyse the clinical characteristics of LCT in a large patient sample and to compare these findings with corresponding data of germ-cell tumours (GCT). Methods In a sample of 208 patients treated during 1995-2017 in 33 institutions, the following characteristics were registered: age, presenting symptoms, primary tumour size, testis-sparing surgery (TSS) or orchiectomy, malignancy, laterality, medical history, and outcome. Data analysis included descriptive statistical methods and logistic regression analysis. Results The ratio LCT:GCT is 1:23 (4.4%). The findings are as follows: median age 41 years, undescended testis 8%, bilateral LCTs 3%, malignant LCT 2.5%, contralateral GCT 2.5%, incidental detection 28%, scrotal symptoms 43%, infertility 18%, elevated estradiol levels 29%. TSS was performed in 56% with no local relapse. Of the patients with malignant LCT, one was cured through surgery. Conclusion LCT is rare, with a relative frequency (relative to GCT) of 1:23. Malignancy is found in 2.5%. LCT and GCT share a number of clinical features, e.g. bilaterality, history of undescended testis, and presenting age. TSS is safe in benign LCT. Surgery is the treatment of choice in malignant LCT.