Abstract PS3-07-23: Survivor plots for quantitated adjunctive statistically standardized ER, PgR, and HER2 in adjuvant postmenopausal breast cancer: Canadian Cancer Trials Group MA.27 trial of exemestane versus anastrozole

Abstract Background: Survivor plots permit adjustment by baseline demographics and clinical characteristics; log-normal survival analysis may be more robust than a Cox model under departures from model assumptions. We depicted distant disease-free survival (DDFS) for statistically standardized quantitated ER, PgR, and HER2. Methods: We utilized CCTG MA.27 (NCT00066573), an adjuvant phase III trial of exemestane versus anastrozole in postmenopausal women with ER+ and/or PgR+ tumours. IHC ER, PgR, and HER2 HSCORE were centrally assessed by machine image quantitation, and statistically standardized to mean of 0, standard deviation (SD) of 1 following Box-Cox variance stabilization transformations of square for ER, natural logarithm (ln) and square root for PgR, and ln for HER2. For the ln transformation, 0.1 was added to 0 HSCOREs for a stable transformation. The primary endpoint was DDFS at the longest trial follow-up of 4.1 years. For log-normal survival analysis, ln(time) is a linear function of covariates and had a normal distribution; the Cox models were log-linear for covariates. Survival was depicted with log-normal and Cox survivor plots adjusted at the means of age, T and N stage, grade, lymphovascular invasion, treatment, and baseline patient demographics. We examined ER and PgR ASCO/CAP cut-points at (0; >0), HER2 cut-points at (IHC 0, 0 stain; IHC 0, (0,10%] stain; IHC 1+; IHC 2+; IHC 3+), and ER/PgR/HER2 standardized cut-points at standard deviations about mean of 0 (<-1; (-1,0]; (0,1]; >1). P was based on the likelihood ratio criterion (∼Χ2 (1)) for the addition of ER/PgR/HER2 to the model of baseline covariates, and had nominal significance if P<0.05. Log-normal and Cox multivariable regressions with unstandardized and standardized categorical, and continuous, ER, PgR, and HER2 were adjusted by baseline covariates; 2-sided Wald tests had nominal significance if P<0.05. Results: Of 7576 MA.27 patients, 2325 patients had quantitated image analysis assessments for ER, PgR, and HER2; 113 of 2325 (4.9%) patients experienced a DDFS event during follow-up. Multivariable log-normal survival analysis indicated DDFS was significantly longer for patients with T1 (p=0.01), N0 (p=.002), and grade 1/2 tumors (p=0.01); similar significance levels were found with a Cox model. Log-normal survivor plots were smooth, while Cox survivor plots were step-wise discontinuous at events. Adjusted log-normal survivor plots indicated similar 5-year DDFS for patients by standardized ER categories (p=0.43): 95.4% for those with ER <-1.0 (n=401); 95.8%, for (-1.0,0.0] (n=737); 96.1%, for (0.0,1.0] (n=737); and 96.4%, for >1.0 (n=450). The log-normal standardized PgR survivor plots indicated patients had significantly different 5-year DDFS (p<.001) by categories, with both ln and square root transformations of HSCORE: with a ln transformation, 93.7% for <-1.0 (n=607); 95.4%, for (-1.0,0.0] (n=390); 96.8%, for (0.0,1.0] (n=826); and 97.8%, for >1.0 (n=502). Patients had similar 5-year DDFS by standardized HER2 categories (p=0.71): 96.2% for <-1.0 (n=83); 96.0%, for (-1.0,0.0] (n=1201); 95.9%, for (0.0,1.0] (n=527); and 95.7%, for >1.0 (n=514). In full fit multivariable log-normal survival analyses, DDFS was not significantly different for ER (p=0.51-0.89) and HER2 (p=0.12-0.98); higher PgR was associated with significantly better DDFS (p=0.01 to <.001). Adjusted Cox survival analyses had similar results. Conclusions: Survivor plots adjusted for baseline demographic and clinical characteristics provided similar indications of significance for standardized ER, PgR, and HER2 as those seen in multivariable models with both log-normal and Cox survival analyses. Higher PgR was associated with significantly better DDFS. Citation Format: J. W. Chapman, J. Bayani, S. SenGupta, J. M. S. Bartlett, T. Piper, M. A. Quintayo, S. Virk, P. E. Goss, J. N. Ingle, M. J. Ellis, G. W. Sledge, G. T. Budd, M. Rabaglio, R. H. Ansari, R. Tozer, D. P. D'Souza, H. Chalchal, S. Spadafora, V. Stearns, E. A. Perez, K. A. Gelmon, T. J. Whelan, C. Elliott, L. E. Shepherd, B. E. Chen, K. J. Taylor. Survivor plots for quantitated adjunctive statistically standardized ER, PgR, and HER2 in adjuvant postmenopausal breast cancer: Canadian Cancer Trials Group MA.27 trial of exemestane versus anastrozole [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-07-23.