Patients with a rising PSA after primary therapy for prostate cancer were enrolled. A PSA doubling time (PSADT) <12 months was required. Lapatinib was administered at 1,500 mg orally daily. Outcome measures were changes in PSA kinetics. Primary tumor blocks were obtained and assessed for EGFR expression, EGFR Q787Q polymorphism, and Kras 38 mutational status.
Forty-nine patients were enrolled (14 ineligible), resulting in 35 patients for analysis. No PSA response was observed; best response was stable disease (n = 28, 80.0 % ). Pretreatment average slope was 0.19 log (PSA)/month (PSADT = 3.70 months), in contrast to on-treatment average slope of 0.13 log (PSA)/month (PSADT = 5.44 months) using linear mixed effects models (P = 0.006). Median progression-free survival (PFS) was 17.4 months for the high EGFR group and 6.0 months for the low EGFR group (P = 0.50). Patients with Kras 38 mutation had shorter PFS than those without Kras 38 mutation (P = 0.09).
Although no PSA responses (primary endpoint) was observed, lapatinib may have biologic activity in men with stage D0 prostate cancer as evidenced by a decrease in PSA slope in this non-randomized study. Additional trials assessing the role of EGFR overexpression and Kras wild type status in prostate cancer should be investigated.