An immunohistochemical signature comprising PTEN, MYC, and Ki67 predicts progression in prostate cancer patients receiving adjuvant docetaxel after prostatectomy.

BACKGROUND

Loss of the tumor suppressor PTEN is common in prostate cancer and may have prognostic significance. The authors examined PTEN and additional protein markers in primary tumors from patients with high-risk, localized prostate cancer who received adjuvant docetaxel in a prospective multicenter trial (TAX2501).

METHODS

Fifty-six of 77 patients enrolled in TAX2501 had primary prostatectomy specimens available for immunohistochemical analysis of PTEN, MYC, ERG, tumor protein p53 (p53), antigen KI-67 (Ki67), and phosphorylated forms of Akt, mammalian target of rapamycin (mTOR), and S6 ribosomal protein. Protocol-defined progression included a prostate-specific antigen (PSA) level ≥ 0.4 ng/mL, radiologic/clinical recurrence, or death. Univariate and multivariable proportional hazards regression analyses were used to investigate the influence of PTEN status (and other protein markers) on progression-free survival (PFS).

RESULTS

In this exploratory, post hoc analysis, PTEN protein loss (vs presence) was observed in 61% of patients and was associated with lower preoperative PSA levels, higher clinical stage, lower Ki67 expression, the presence of p53, and the presence of ERG. In univariate analysis, the factors associated with PFS included Gleason sum, seminal vesicle invasion, PTEN status, MYC expression, and Ki67 expression. In multivariable analysis, only 3 variables emerged as independent prognostic factors for PFS: PTEN status (P = .035), MYC expression (P = .001), and Ki67 expression (P < .001). A prognostic model was constructed that incorporated clinical covariates as well as information on PTEN, MYC, and Ki67.

CONCLUSIONS

The current results indicated that PTEN status, MYC expression, and Ki67 expression in primary tumor samples may predict PFS more accurately than clinical factors alone in men with high-risk prostate cancer who receive adjuvant docetaxel after prostatectomy. If validated, these hypothesis-generating findings may have prognostic and therapeutic implications and may aid clinical trial design.