The increasing potency of therapies that target the androgen receptor (AR) signalling axis has correlated with a rise in the proportion of patients with prostate cancer harbouring an adaptive phenotype, termed treatment-induced lineage crisis. This phenotype is characterized by features that include soft-tissue metastasis and/or resistance to standard anticancer therapies. Potent anticancer treatments might force cancer cells to evolve and develop alternative cell lineages that are resistant to primary therapies, a mechanism similar to the generation of multidrug-resistant microorganisms after continued antibiotic use. Herein, we assess the hypothesis that treatmentadapted phenotypes harbour reduced AR expression and/or activity, and acquire compensatory strategies for cell survival. We highlight the striking similarities between castration-resistant prostate cancer and triple-negative breast cancer, another poorly differentiated endocrine malignancy. Alternative treatment paradigms are needed to avoid therapy-induced resistance. Herein, we present a new clinical trial strategy designed to evaluate the potential of rapid drug cycling as an approach to delay the onset of resistance and treatment-induced lineage crisis in patients with metastatic castration-resistant prostate cancer.Potent clinical suppression of androgen receptor (AR) signalling has been achieved with the pharmacological inhibitors abiraterone acetate 1,2 and enzalutamide 3,4 (drugs that were approved by the FDA in 2011 and 2014, respectively), resulting in significant survival benefits for men with metastatic castration-resistant prostate cancer (mCRPC). Emerging evidence suggests, however, that the prolonged therapeutic use of abiraterone and enzalutamide induces adaptive clinical phenotypes -including histological dedifferentiation and lineage alterations, such as treatment-induced neuroendocrine prostate cancer (t-NEPC) 5 and treatment-induced epithelial-to-mesenchymal transition 6,7 (t-EMT) (BOX 1). Such resistant phenotypes, in turn, might cause aggressive visceral metastases, a trend that has been reported with increasing prevalence in patients with prostate cancer who have received long-term androgen deprivation therapy (ADT) 5,[8][9][10][11][12] . While the mechanisms Correspondence to D.J.M. david.mulholland@mssm.edu. Author contributions: G.R. and D.J.M researched data and wrote the manuscript. All authors discussed the article's contents, revised and edited the manuscript before submission. B.C.L. and W.K.O. designed the PRINT clinical protocol.
Competing interests statement:The authors declare no competing interests. Increased research emphasis should be placed on the development of preclinical models, in which the effects of treatment-induced resistance can be tested directly, as well as on the development of alternative treatment strategies that could be used to prolong the survival of men with advanced-stage prostate cancer by delaying the onset of resistance and minimizing toxicities. We suggest a new treatment approach, ...