490PResponse rates and lesion-level progression patterns of solid tumor patients in an academic phase I program: implications for tumour heterogeneity

Abstract Background Sequencing studies have demonstrated extensive genetic heterogeneity between and within tumor lesions in treated metastatic solid tumor patients. The response of individual tumor lesions to therapy is a reflection of subclonal inhibition and growth in the face of selective pressure. Are there lesion-level progression patterns that would provide insights into the biological heterogeneity that underpins response and resistance?. Methods Retrospective review of patients with histologically confirmed metastatic solid tumors who were treated at Massachusetts General Hospital Cancer Center’s phase 1 center from October 1, 2010 to September 30, 2015 and had at least two radiographic assessments, 30 days apart. 769 study participants were enrolled in a phase 1 trial during the study period, of which 575 had at least two radiographic evaluations. 427 participants had more than one lesion at baseline and displayed progression of at least one lesion (growth of at least 20% or a new lesion). We categorized the lesion-level progression patterns of these 427 patients. Results Study participants had a mean of 2.6 prior lines of therapy in the metastatic setting with an average of 6.3 tumor lesions on their baseline scan involving an average of 3 organs. Of the 427 study patients with progressive lesions, 24% of patients had progression at a single lesion and 49% of patients had progression in a single organ when they were taken off-study or at data cut-off. 10% of patients exhibited simultaneous response (shrinkage of at least 30%) and progression in different lesions. Across our entire 575 patient cohort, liver lesions were 2.9 times as likely to progress than other lesions regardless of cancer types. Conclusions The significant proportion of patients with progression at a single lesion or organ demonstrates that clonal heterogeneity has important clinical implications. Liver lesions may have microenvironment-specific factors that increase the likelihood of progression relative to other organ sites. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure C. Chen: Advisory / Consultancy: Blackstone Life Sciences; Advisory / Consultancy: HotSpot Therapeutics; Advisory / Consultancy: Foundation Medicine. D. Juric: Advisory / Consultancy: Novartis; Advisory / Consultancy: Genentech; Advisory / Consultancy: Eisai; Advisory / Consultancy: Syros; Advisory / Consultancy: Ipsen; Research grant / Funding (self): Eisai; Research grant / Funding (self): Genentech; Research grant / Funding (self): Celgene; Research grant / Funding (self): Takeda; Research grant / Funding (self): javascript:%20create_table_line(’1’,%20new%20Array(’ent’,%20’des’,%20’tor’));Celgene; Research grant / Funding (self): Placon Therapeutics; Research grant / Funding (self): Syros; Research grant / Funding (self): EMD Serono; Research grant / Funding (institution): Novartis. All other authors have declared no conflicts of interest.