Abstract 5451: Longitudinal proteomic assessment of patient with metastatic apocrine adenocarcinoma reveals evolutionary selection for androgen-receptor-dependence and therapeutic response

Combined use of new molecular diagnostic and imaging methods could improve care of individual patients with rare cancers. A 57-year-old developed apocrine adenocarcinoma of the left axilla with regional lymph node metastasis detected at initial surgery. After adjuvant regional radiotherapy, metastases developed and over the subsequent 7 years he received serial systemic therapy with 11 different regimens. Expression of 128 proteins/phosphoproteins was evaluated in 8 tissue samples from diagnosis, progressive adenopathy at 45 months, brain metastases at 60 months, and abdominal metastases at 63 months by CLIA-standardized reverse phase phosphoprotein arrays (RPPA). Tumor burden was estimated by quantifying the volume of individual lesions with semi-automated segmentation algorithms on serially collected CT images. Next-generation sequencing (NGS) revealed a PIK3CA K111T mutation, prompting treatment with sirolimus 28 months after diagnosis. Seventeen months later, new neoplastic adenopathy emerged. NGS revealed a new PIK3CA M610V mutation. Semiquantitative scoring of RPPA demonstrated relative increase in AKT (from 0.72 to 0.9) and mTOR (from 0.55 to 0.8) pathway activation. The relative estimated tumor burden (RETB) was 21,145 mm3. Over 6 months of docetaxel therapy the RETB decreased to 12,077 mm3. The patient subsequently received pembrolizumab with increased RETB (71,308 mm3). Gemcitabine appeared to stabilize the RETB (73,168 mm3), but brain metastases emerged. The patient underwent craniotomy, began paclitaxel therapy, and then RETB declined to 35,623 mm3. But new symptomatic abdominal metastases prompted surgical resection. The patient then received the PI3K inhibitor taselisib; however, after an initial decrease, RETB rose to 31,208 mm3. At this point, the patient began bicalutamide therapy. NGS of the primary mass and the initial metastatic adenopathy revealed no amplification of the androgen receptor (AR). But RPPA demonstrated inversion of the ratio of measured phosphorylated AR S81 to AR S650, suggesting primarily cytoplasmic AR in tumor through 45 months but nuclear AR in samples resected at 60 and 63 months. Immunohistochemistry revealed 3+ nuclear AR expression in the latter metastatic tissue. After 9 months of bicalutamide, enzalutamide and leuprolide were administered for 7 months (final RETB = 1,555 mm3). Treatment continued beyond the study period. Tumor burden assessment by new CT imaging measurement methods, combined with RPPA could improve adaptive, responsive, therapy for patients with rare tumors. We identified the phenotypic evolution of androgen-driven growth of apocrine adenocarcinoma after cytotoxic and PI3K-mTOR inhibitor therapy. Protein-based diagnostics revealed an effective treatment strategy in late metastatic disease that was not indicated by NGS testing. Citation Format: Erik Dvergsten, Anthony Serritella, Danielle Kimble, Malcom McIver, Sanja Karovic, Vasiliki Thomeas-McEwing, Hao Yang, Manish R. Sharma, Thomas P. Conrads, Mariaelena Pierobon, Peter Pytel, Binsheng Zhao, Lawrence H. Schwartz, Emanuel F. Petricoin, Russell Szmulewitz, Michael L. Maitland. Longitudinal proteomic assessment of patient with metastatic apocrine adenocarcinoma reveals evolutionary selection for androgen-receptor-dependence and therapeutic response [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5451.