Personalized Medicine and Imaging High-Risk Premenopausal Luminal A Breast Cancer Patients Derive no Benefit from Adjuvant Cyclophosphamide-based Chemotherapy: Results from the DBCG77B Clinical Trial Torsten O. Nielsen 1 , Maj-Brit Jensen 2 , Samantha Burugu 1 , Dongxia Gao 1 , Charlotte L. Tykjaer Jørgensen 2 , Eva Balslev 2 , and Bent Ejlertsen 2 Abstract Purpose: Luminal A breast cancers have better prognosis than other molecular subtypes. Luminal A cancers may also be insen- sitive to adjuvant chemotherapy, although there is little high-level evidence to confirm this concept. The primary hypothesis in this formal prospective–retrospective analysis was to assess interac- tion between subtype (Luminal A vs. other) and treatment (che- motherapy vs. not) for the primary endpoint (10-year invasive disease-free survival) of a breast cancer trial randomizing women to adjuvant chemotherapy, analyzed in multivariate Cox propor- tional hazards models using the Wald interaction test. Experimental Design: The Danish Breast Cancer Cooperative Group 77B clinical trial randomized 1,072 premenopausal women to no systematic treatment (control), levamisole, cyclophospha- mide, or cyclophosphamide–methotrexate–fluorouracil arms. All arms included radiotherapy but no endocrine therapy. Researchers with no access to clinical data performed intrinsic subtype analysis on tissue microarrays using published immunohistochemical methods based on estrogen receptor, progesterone receptor, HER2, Ki67, and basal markers. Results: Patients (n ¼ 709) had tissue available; chemotherapy benefit in these patients was similar to the original trial (HR, 0.56). Immunohistochemistry classified 165 as Luminal A, 319 Luminal B, 58 HER2-enriched, and 82 core basal (among 91 triple-negative). Patients with Luminal A breast tumors did not benefit from chemotherapy [HR, 1.06; 95% confidence interval (CI), 0.53–2.14; P ¼ 0.86], whereas patients with non–luminal A subtypes did (HR, 0.50; 95% CI, 0.38-0.66; P < 0.001; P interaction ¼ 0.048). Conclusions: In a prospective–retrospective analysis of a ran- domized trial, patients with Luminal A breast cancers did not benefit from adjuvant cyclophosphamide-based chemotherapy. Clin Cancer Res; 23(4); 946–53. Ó2016 AACR. Introduction The Luminal A, Luminal B, HER2-enriched (HER2E), and basal-like intrinsic molecular subtypes of breast cancer were initially discovered on microarrays (1) but can be detected with reasonable accuracy using immunohistochemistry panels (2, 3). Of particular clinical importance is the Luminal A subtype, characterized by high expression of estrogen and progesterone receptors (ER, PR) but low expression of proliferation markers (4). Multiple studies have demonstrated the good prognosis of Luminal A tumors, including formal prospective-retrospective studies of clinical trials where women received endocrine therapy but not chemotherapy (5, 6). Conventional chemotherapies target replicating cells, and Luminal A tumors express low levels of proliferation genes, providing a theoretical basis for the concept that Luminal A status might predict lack of chemotherapy benefit. While cohort and neoadjuvant studies support this concept (7, 8), the highest level of evidence requires formal interaction testing on clinical trials randomizing women to chemotherapy versus no chemotherapy, against survival endpoints. However, material from such trials is difficult to obtain. The benefit of adjuvant chemotherapy was proven by randomized trials reported in the 1980s (9); since then, most breast cancer studies have random- ized among different chemotherapy regimens without includ- ing no-chemotherapy arms. The relevant older studies generally did not retain tissue blocks; even among the few that did, collection was incomplete and/or materials were consumed for other studies (10), rendering modern biomarker subset anal- yses underpowered. Some materials were available from Danish Breast Cancer Cooperative Group (DBCG) trial 77B, which demonstrated that classical cyclophosphamide–methotrexate–fluorouracil (CMF) and oral single-agent cyclophosphamide (C) significantly reduce recurrence and mortality in premenopausal patients with high- risk early breast cancer treated after effective local therapy (11). Similar results were observed in the first adjuvant Milan trial and NSABP B-20, all consistent with the Early Breast Cancer Trialists' Collaborative Group meta-analysis (12–14). The survival gain was fostered 5 to 10 years after randomization and persisted 1 Genetic Pathology Evaluation Centre, University of British Columbia, Vancou- ver, Canada. 2 Danish Breast Cancer Cooperative Group, Copenhagen, Denmark. Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/). Corresponding Author: Torsten O. Nielsen, University of British Columbia, JPN 1401, 855 W. 12 th Avenue, Vancouver BC, Canada V5Z 1M9. Phone: 1-604-8754111, ext. 66768; Fax: 1-604-8754797; E-mail: torsten@mail.ubc.ca doi: 10.1158/1078-0432.CCR-16-1278 Ó2016 American Association for Cancer Research. Clinical Cancer Research Clin Cancer Res; 23(4) February 15, 2017 946 on June 7, 2020. © 2017 American Association for Cancer Research. clincancerres.aacrjournals.org Downloaded from Published OnlineFirst September 6, 2016; DOI: 10.1158/1078-0432.CCR-16-1278