ONCOmmunity

Activating AKT1 and PIK3CA Mutations in Metastatic Castration-Resistant Prostate Cancer.

By: Cameron Herberts, Andrew J Murtha, Simon Fu, Gang Wang, Elena Schönlau, Hui Xue, Dong Lin, Anna Gleave, Steven Yip, Arkhjamil Angeles, Sebastien Hotte, Ben Tran, Scott North, Sinja Taavitsainen, Kevin Beja, Gillian Vandekerkhove, Elie Ritch, Evan Warner, Fred Saad, Nayyer Iqbal, Matti Nykter, Martin E Gleave, Yuzhuo Wang, Matti Annala, Kim N Chi, Alexander W Wyatt

Vancouver Prostate Centre, Department of Urologic Sciences, University of British Columbia, Vancouver, BC, Canada.
2020-01-20; doi: 10.1016/j.eururo.2020.04.058

Abstract

Background

Activating mutations in AKT1 and PIK3CA are undercharacterised in metastatic castration-resistant prostate cancer (mCRPC), but are linked to activation of phosphatidylinositol 3-kinase (PI3K) signalling and sensitivity to pathway inhibitors in other cancers.

Objective

To determine the prevalence, genomic context, and clinical associations of AKT1/PIK3CA activating mutations in mCRPC.

Design,

We analysed targeted cell-free DNA (cfDNA) sequencing data from 599 metastatic prostate cancer patients with circulating tumour DNA (ctDNA) content above 2%.

Outcome

In patients with AKT1/PIK3CA mutations, cfDNA was subjected to PTEN intron sequencing and matched diagnostic tumour tissue was analysed when possible.

Results

Of the patients, 6.0% (36/599) harboured somatic clonal activating mutation(s) in AKT1 or PIK3CA. Mutant allele-specific imbalance was common. Clonal mutations in mCRPC ctDNA were typically detected in pretreatment primary tissue and were consistent across serial ctDNA collections. AKT1/PIK3CA-mutant mCRPC had fewer androgen receptor (AR) gene copies than AKT1/PIK3CA wild-type mCRPC (median 4.7 vs 10.3, p = 0.003). AKT1 mutations were mutually exclusive with PTEN alterations. Patients with and without AKT1/PIK3CA mutations showed similar clinical outcomes with standard of care treatments. A heavily pretreated mCRPC patient with an AKT1 mutation experienced a 50% decline in prostate-specific antigen with Akt inhibitor (ipatasertib) monotherapy. Ipatasertib also had a marked antitumour effect in a patient-derived xenograft harbouring an AKT1 mutation. Limitations include the inability to assess AKT1/PIK3CA correlatives in ctDNA-negative patients.

Conclusions

AKT1/PIK3CA activating mutations are relatively common and delineate a distinct mCRPC molecular subtype with low-level AR copy gain. Clonal prevalence and evidence of mutant allele selection propose PI3K pathway dependency in selected patients. The use of cfDNA screening enables prospective clinical trials to test PI3K pathway inhibitors in this population.

Patient

Of advanced prostate cancer cases, 6% have activating mutations in the genes AKT1 or PIK3CA. These mutations can be identified using a blood test and may help select patients suitable for clinical trials of phosphatidylinositol 3-kinase inhibitors.