PTEN is a negative regulator of PI3K/AKT signaling. PI3K/AKT signaling can be activated by HER2, and it has been hypothesized that alteration in this pathway may affect sensitivity to trastuzumab (Herceptin). Preclinical data and some of the limited available clinical data suggest that loss or inactivation of PTEN, which has been reported in a significant proportion of HER2-positive breast cancers, may result in reduced sensitivity to trastuzumab.

In an analysis reported in Journal of Clinical Oncology, Edith A. Perez, MD, Deputy Director at Large, Mayo Clinic Cancer Center, and Group Vice Chair, Alliance for Clinical Trials in Oncology, Mayo Clinic, Jacksonville, Florida, and colleagues found that disease-free survival among patients with early-stage breast cancer receiving adjuvant trastuzumab in the North Central Cancer Treatment Group N9831 trial did not significantly differ according to PTEN status.¹

Study Details

In the N9831 trial, women with early-stage HER2-positive breast cancer received doxorubicin and cyclophosphamide followed by weekly paclitaxel (control group) or the same regimen followed by 1 year of sequential trastuzumab or concurrent trastuzumab (started on the same day as paclitaxel). Patents receiving trastuzumab had significantly better disease-free survival and overall survival compared with the control group, and patients receiving concurrent trastuzumab had significantly better disease-free survival than those receiving sequential trastuzumab.

The current analysis of the effect of PTEN status included 1,802 of the 3,505 patients registered in N9831, with reasons for exclusion consisting of absence of HER2-positivity on central pathology review, withdrawal before starting therapy, failure to meet eligibility criteria, no consent for future translational analysis, withdrawn consent/loss to follow-up, no or inadequate tumor tissue, and technical failure. Clinic pathologic characteristics and outcomes in the 1,802 patients from the three treatment groups included in the analysis (601 in control group, 650 in sequential trastuzumab group, and 551 in concurrent trastuzumab group) were similar to excluded patients in the three treatment groups.

To determine PTEN status, the intensity and percentage of invasive cells with cytoplasmic PTEN staining were determined in tissue microarray sections with three cores per block (n = 1,286) or in whole tissue sections (n = 516) using standard immunohistochemistry (IHC). Tumors were considered PTEN-positive if any core or whole tissue section had any invasive cells with IHC ≥ 1+ staining. In the primary analysis, outcomes were assessed according to PTEN-negative status defined as IHC 0 staining; outcomes were also assessed according to PTEN-negative status defined as IHC 0–1 staining.

Characteristics of PTEN-positive Cases

Of 1,802 patients, 1,342 (74%) had PTEN-positive tumors (≥ 1+ staining) and 460 (26%) had PTEN-negative tumors (0 cytoplasmic staining). Of those with PTEN-positive tumors, 650 had 1+ staining, 523 had 2+ staining, and 169 had 3+ staining.

Patients with PTEN-positive tumors defined as ≥ 1+ staining had a lower rate of hormone receptor positivity (45% vs 55%, P < .001) and a higher rate of nodal positivity (87% vs 83%, P = .04) compared with PTEN-negative patients. However, when PTEN positivity was defined as 2–3+ staining, patients with PTEN-positive tumors had a higher rate of hormone receptor positivity (60% vs 48%, P < .001) but still had a higher rate of nodal positivity (90% vs 83%, P < .001).

Disease-free Survival Outcomes

Median follow-up of patients in the analysis was 6.0 years. There were no significant differences in disease-free survival between patients with PTEN-positive vs PTEN-negative tumors defined as IHC 0 staining among all patients (hazard ratio [HR] = 0.96, P = .70) or within the control (HR = 0.92, P = .64), sequential trastuzumab (HR = 0.81, P = .27), or concurrent trastuzumab (HR = 1.40, P = .20) groups.

For the concurrent trastuzumab group compared with the control group, hazard ratios for disease-free survival were 0.65 (P = .003) for those with PTEN-positive tumors and 0.47 (P = .005; P = .16 for interaction) for those with PTEN-negative tumors defined as IHC 0. For the sequential trastuzumab group compared with the control group, hazard ratios were 0.70 (P = .009) for those with PTEN-positive tumors and 0.85 (P = .44; P = .47 for interaction) for those with PTEN-negative tumors. For the concurrent trastuzumab group compared with the sequential group, hazard ratios were 0.90 (P = .49) for those with PTEN-positive tumors and 0.56 (P = .04; P = .08 for interaction) for those with PTEN-negative tumors.

When PTEN-negativity was defined as IHC 0–1 staining, there were no significant differences in disease-free survival for PTEN-positive vs PTEN-negative patients among all patients (HR = 0.96, P = .70) or within the control (HR = 0.87, P = .38), sequential trastuzumab (HR = 0.79, P = .19), or concurrent trastuzumab (HR = 1.27, P = .25) groups.

For the concurrent trastuzumab group compared with the control group, hazard ratios for disease-free survival were 0.70 (P = .08) for those with PTEN-positive tumors and 0.50 (P < .001; P = .17 for interaction) for those with PTEN-negative tumors. For the sequential trastuzumab group compared with the control group, hazard ratios were 0.68 (P = .04) for those with PTEN-positive tumors and 0.78 (P = .08; P = .61 for interaction) for those with PTEN-negative tumors. For the concurrent trastuzumab group compared with the sequential group, hazard ratios were 1.01 (P = .95) for those with PTEN-positive tumors and 0.66 (P = .02; P = .10 for interaction) for those with PTEN-negative tumors.

Benefit of Trastuzumab Independent of PTEN Status

As summarized by the investigators, “In contrast to the hypothesis that PTEN loss is correlated with poor prognosis and decreased survival, our carefully conducted study demonstrated a lack of correlation of PTEN expression with outcome of N9831 patients. The disease-free survival of patients within each treatment arm was not significantly different between patents with PTEN-positive and PTEN-negative tumors. We observed a benefit of concurrent trastuzumab compared with chemotherapy alone in all patients, independent of tumor PTEN expression.” They further noted, “Our results in the adjuvant setting appear to conflict with a somewhat general consensus that PTEN loss correlates with trastuzumab resistance, although it is important to note that previously available correlative data have been inconsistent as well.”

The investigators concluded, “Overall, the N3981 data indicate that PTEN protein expression alone (independent of cut point) is not significantly associated with prognosis or with differential benefit to concurrent trastuzumab. Importantly, the conflicting results obtained between this study in the adjuvant setting and some (not all) of the reported small studies in the metastatic and neoadjuvant settings highlight the need for accurate validation of biomarkers in large patient groups….”

The investigators are continuing protein expression and whole-genome expression profiling studies in tumors from patients in the N9831 trial to examine associations between combinations of markers and disease-free survival. By doing so, they hope to improve understanding of the effects of signaling pathway alterations on outcomes with adjuvant trastuzumab and chemotherapy. ■

Disclosure: Dr. Perez has received research funding from Genentech and GlaxoSmithKline. For full disclosures of all study authors, see jco.ascopubs.org.

Reference

1. Perez EA, Dueck AC, McCullough AE, et al: Impact of PTEN protein expression on benefit from adjuvant trastuzumab in early-stage human epidermal growth factor receptor 2-positive breast cancer in the North Central Cancer Treatment Group N9831 trial. J Clin Oncol 31:2115-2122, 2013.