Finally, treatment with the PRMT5 small molecule inhibitor pemrametostat and the ER degrader fulvestrant synergistically suppressed growth of ER+/RB-deficient xenografts derived from cell lines and patients, suggesting dual ER and PRMT5 blockade as a novel therapeutic strategy to treat ER+/RB-deficient breast cancer. The gene discussed is RB1; the disease is breast carcinoma.