Abstract P2-08-01: PIK3CA mutations associate with decreased Ki67 in early stage breast cancer (BC) and better outcomes in patients even among those with low Ki67 tumors.

Abstract Background: In studies of over 450 BC patients (pts) with &amp;gt; 10 years follow-up, pts with PIK3CA-mutated primary tumors had improved clinical outcome (Kalinsky et al 2009, Cizkova et al 2012). PIK3CA mutations associated with favorable clinicopathologic features: lower grade, smaller size, lymph node negativity (−), ER positivity (+), HER2−. In BC, several studies have suggested that PIK3CA mutations do not associate with PI3K/mTOR pathway activation (Loi et al 2010, Stemke-Hale et al 2008). To gain additional insight into the favorable biology imparted by a PIK3CA mutation in early stage BC and to identify predictive biomarkers, we performed immunohistochemistry (IHC) on tissue microarrays (TMA) constructed from 590 primary BCs. Methods: TMAs derived from FFPE tumors previously genotyped for PIK3CA mutations (rate of 32.5%, 192/590) were stained for ER, HER2 and AR (Kalinsky et al 2009). Here, we performed additional stains for MIB1 (Ki67 proliferation index, Ki67), p53 and markers of PI3K pathway activation (pS6, PTEN). Slides were scanned with Aperio ScanScope XT and segmented using TMALab (Aperio). Images were analyzed with the Aperio algorithm based on staining pattern (nuclear, cytoplasmic, membrane) and scored for % + and intensity. Manual review was performed for tumors with less than 3 cores or discordant results. PTEN was scored manually: 0 (no tumor staining, PTEN loss), 1 (tumor &amp;lt; stroma), or 2 (tumor ≥ stroma). P values were based on the log-rank test for comparison of Kaplan-Meier curves for disease free survival (DFS), Chi-square test for categorical variables and t-test for continuous variables. Results: On average, 66 cases (11%) were non-informative for each IHC stain, due to missing cores or insufficient tumor cells. In a binary analysis of Ki67 using a cutoff of ≥10% + cells, PIK3CA mutated tumors demonstrated significantly lower proliferation index with only 9.4% of tumors (16/170) having high Ki67 as compared to 23.6% of wild-type PIK3CA tumors (82/347) (P = .001). Ki67 was also highly associated with PIK3CA genotype when analyzed with a cutoff of ≥13.25% + cells or as a continuous variable. Importantly, DFS was significantly different when analyzed by PIK3CA genotype and Ki67 (P = .01). Among pts with low Ki67 tumors (n = 419), PIK3CA mutation associated with longer DFS (10yr 79%, CI 69–85) as compared to wild-type PIK3CA (10yr 71%, CI 64–77). When PI3K pathway interactions were analyzed, PTEN loss associated with wild-type PIK3CA (P&amp;lt;.001), although PTEN loss occurred with mutated PIK3CA in 11 hormone receptor (HR)+ tumors. In analysis of pS6 with a binary cutoff of ≥20% + cells, high pS6 associated with HER2+ (P&amp;lt;.001), HR- (P&amp;lt;.001) and high tumor grade (P = 0.003), but did not associate with PIK3CA genotype (P = .13). PIK3CA mutation was associated with lower pS6 when pS6 % + cells was analyzed as a continuous variable (P = .01). Conclusions: PIK3CA mutation associates with lower Ki67 in early stage BC. Even among pts with low Ki67 tumors, PIK3CA mutation associates with improved clinical oucome. pS6 is not increased in PIK3CA-mutated tumors which likely indicates that mTORC1 signaling is not activated as a result of PIK3CA mutation in early stage ER+ BC. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-08-01.</jats:p

Abstract P6-05-01: Evaluation of the prognostic significance of androgen receptor (AR) expression in relation to ER expression in breast cancer (BC)

Abstract Background: AR is expressed in 60–80% of invasive BC. Emerging data suggest that AR expression may have a prognostic role in BC irrespective of ER and that the androgen-signaling pathway may be involved in BC pathogenesis. We previously identified an AR-dependent subset of ER/PR(−) BC and reported clinical benefit from AR-inhibition (Gucalp, ASCO 2012). We now describe the prevalence, clinicopathologic characteristics, and survival outcomes of AR(+) BC in relation to expression of ER in a single-institution retrospective cohort. Methods: We identified 590 patients (pts) with resectable BC (tumor &amp;gt;1cm) who had surgery at MSKCC from 1992–1996. IRB approval was obtained. Tissue microarray (TMA) construction/scoring has been described (Kalinsky CCR 2009). TMAs were stained, scanned and digitally scored (Aperio ScanScope XT) for nuclear steroid receptors (ER, AR), HER2, p53, and MIB1 (Ki67). Using digital quantification of tumor cell nuclear staining, pts were categorized into the following 7 groups: ER dominant (ERD, both ER and AR &amp;gt;10% with ER&amp;gt;AR by &amp;gt;5%), ER only (ER&amp;gt;10%, AR &amp;lt;10%), ER=AR (both &amp;gt;10%, &amp;lt;5% difference), AR dominant (ARD, both &amp;gt;10%, AR&amp;gt;ER by &amp;gt;5%), AR only (AR&amp;gt;10%, ER&amp;lt;10%), hormone receptor negative (HRN, both &amp;lt;10%) and unknown. Due to small pt numbers, ER=AR and ARD data were combined as were AR only and HRN. Associations between IHC expression and clinicopathologic features were assessed using the Chi-square/t-test. The Kaplan-Meier method, Cox proportional hazards models, and log-rank test were used to evaluate the association of IHC expression category on disease-free survival (DFS), distant (d)-DFS, and overall survival (OS). Results: 528 pts had adequate tumor cores for image analysis/quantification of AR; 302 (57%) tested AR(+). Median followup 12.8 years (yr). A significant difference in DFS (P = .0145), d-DFS (P = .006) and OS (P = .0485) was observed among the following groups: ERD, ER only, ER=AR/ARD and HRN/AR only, with a more favorable outcome associated with ERD (Table 1). In ER+ BC, ER=AR and ARD are associated with a high frequency of tumor MIB1, p53 and HER2 over-expression (Table 2). Conclusions: The degree of AR expression relative to ER may be prognostic as survival appears attenuated when AR is the more highly expressed steroid transcription factor. Other poor prognostic factors, including p53, HER2 and higher proliferation indices associate with this finding. The biology associated with AR dominance in ER+ BC needs further study. The inferior clinical outcome of the ER only category is in agreement with recent reports. Further analysis of PIK3CA mutational status and PI3K signaling pathway activation in relation to AR is ongoing. Supported in part by Geoffrey Beene Cancer Research Center at MSKCC. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-05-01.</jats:p

Abstract P2-16-07: Phase II study of pertuzumab, trastuzumab, and weekly paclitaxel in patients with metastatic HER2-overexpressing metastatic breast cancer with cardiac biomarker data

Abstract Background: Pertuzumab (P), a monoclonal antibody that binds to extracellular domain II of HER2 distally from trastuzumab (H), disrupts HER2 dimerization and signaling. Dual anti-HER2 therapy with HP + docetaxel in HER2+ metastatic breast cancer (MBC) prolonged progression-free survival (PFS) in the placebo-controlled CLEOPATRA phase III trial. We report matured results of a phase II study to evaluate the efficacy and cardiac safety of weekly paclitaxel with HP (THP). Methods: Patients (pts) with HER2+ MBC with 0-1 prior treatment (Rx) were eligible. Pts received weekly (w) paclitaxel (80mg/m2), q3w trastuzumab (loading dose 8mg/kg → 6mg/kg), and q3w pertuzumab (flat loading dose 840mg → flat dose 420mg). The primary endpoint was PFS at 6 months (mo). Secondary endpoints included response, safety (including cardiac events), and tolerability. Evaluable pts were those who had started study Rx and were able to be assessed at 6 mo for PFS. Safety and toxicity are reported for all enrolled patients. Left ventricular ejection fraction (LVEF) was monitored by echocardiogram (ECHO) every 3 mo. Cardiac enzymes including troponin I (TNI) and brain natriuretic peptide (BNP) were measured every other cycle x6. Cardiac events (CE) were defined as symptomatic LV systolic dysfunction (LVSD), non-LVSD cardiac death, or probable cardiac death. Results: As of June 10th 2013, 63 pts were enrolled; 50 pts have reached the primary endpoint and were assessed at 6 mo for PFS. At 6 mo, 38/50 pts (76%) are progression-free (5 CR, 20 PR and 13 SD); 9 pts progressed; 3 pts were non-evaluable. The 6 mo PFS results for all patients will be updated. Of all enrolled pts (n = 63), median age was 52 years (range 26 to 72). A total of 28 pts (44%) previously received H in the adjuvant or metastatic setting, and 15 pts (24%) were being treated in the second-line metastatic setting. Safety and toxicity were assessed in all enrolled patients; G 3/4 toxicities were fatigue (3 pts, 5%), neutropenia (3 pts, 5%), peripheral neuropathy (2 pts, 3%), diarrhea (1 pt, 2%), hypomagnesium (1 pt, 2%), sepsis (1 pt, 2%), cellulitis (1 pt, 2%), and dry skin (1 pt, 2%). There were no febrile neutropenic (FN) events. Median LVEF was 64% at baseline (range 50% to 72%), 64% at 3mo (range 50% to 73%), 63% at 6mo (range 49% to 68%), 63% at 9 mo (range 47% to 68%), 64% at 12 mo (range 52% to 69%), 63% at 15 mo (range 55% to 69%), and 63% at 18 mo (range 56% to 68%). There were no CEs and no significant changes in TNI levels. Only 1 pt had a transient rise in BNP after cycle 1, but she did not have a CE. Conclusions: Six-month PFS is 76% (95% CI 62-87%) in evaluable pts. Treatment is safe, with few grade 3/4 toxicities, no FN events, no CEs, and no significant or persistent elevation in TNI or BNP, respectively. THP is endorsed by the NCCN as a treatment option for pts with HER2+ MBC, as supported by this study. This study also suggests that intense serial LVEF monitoring may not be necessary with THP based on the cardiac safety results. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-07.</jats:p