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ASCO believes that high-quality observational studies can advance evidence-based practice for cancer care and are complementary to randomized controlled trials (RCTs). Observational studies can generate hypotheses by evaluating novel exposures or biomarkers and by revealing patterns of care and relationships that might not otherwise be discovered. Researchers can then test these hypotheses in RCTs. Observational studies can also answer or inform questions that either have not been or cannot be answered by RCTs. In addition, observational studies can be used for postmarketing surveillance of new cancer treatments, particularly in vulnerable populations. The incorporation of observational research as part of clinical decision making is consistent with the position of many leading institutions. ASCO identified five overarching recommendations to enhance the role of observational research in clinical decision making: (1) improve the quality of electronic health data available for research, (2) improve interoperability and the exchange of electronic health information, (3) ensure the use of rigorous observational research methodologies, (4) promote transparent reporting of observational research studies, and (5) protect patient privacy.

3 Background: There is a clear need to develop a clinically relevant molecular subtyping approach for prostate cancer. We hypothesized that prostate cancer can be subtyped based on luminal versus basal lineage. Methods: We applied the PAM50 classifier, which is used clinically to identify luminal and basal cancers in breast cancer, to subtype a total of 3,782 prostate cancer samples using a high-density microarray platform run in a CLIA-certified laboratory. We examined the associations of these subtypes and clinical outcomes. Results: We demonstrate that PAM50 segregates prostate cancer into three reproducible subtypes in both retrospective cohorts and on prospective validation: luminal A (33.3%-34.3%), luminal B (28.5%-32.6%), and basal (34.1%-37.1%). Luminal B prostate cancers exhibited the worst clinical prognoses, followed by basal and luminal A subtypes (10-year biochemical recurrence-free survival: 29/39/41%; distant metastasis-free survival: 53/73/73%; prostate cancer-specific survival: 78/86/89%; overall survival: 69/80/82% respectively) on both univariable and multivariable analyses accounting for standard clinicopathologic prognostic factors. Known luminal lineage markers, such as NKX3.1 and KRT18, and the basal lineage CD49f signature, were enriched in luminal- and basal-like cancers respectively, demonstrating the connection between these subtypes and established prostate cancer biology. While both luminal-like subtypes were associated with increased AR expression and signaling, only luminal B prostate cancers were significantly associated with post-operative response to androgen deprivation therapy (ADT) in a subset analysis matching patients based on clinicopathologic variables (interaction p = 0.006, luminal B 10-year metastasis: 33% (treated) vs. 55% (untreated), non-luminal B: 37% (treated) vs. 21% (untreated)). Conclusions: These findings contribute novel insight into the biology of prostate cancer, and provide translatable clinical tools for personalizing post-operative ADT for patients with prostate cancer. Similar to breast cancer, these findings suggest that luminal/basal subtyping may be useful in treatment selection in prostate cancer.

Poly(GP) proteins are a promising pharmacodynamic marker for developing and testing therapeutics for treating C9ORF72 -associated amyotrophic lateral sclerosis.

While elevated blood cholesterol has been associated with an increased risk of colorectal cancer (CRC) in observational studies, causality is uncertain. Here we apply a Mendelian randomisation (MR) analysis to examine the potential causal relationship between lipid traits and CRC risk. We used single nucleotide polymorphisms (SNPs) associated with blood levels of total cholesterol (TC), triglyceride (TG), low‐density lipoprotein (LDL), and high‐density lipoprotein (HDL) as instrumental variables (IV). We calculated MR estimates for each risk factor with CRC using SNP‐CRC associations from 9,254 cases and 18,386 controls. Genetically predicted higher TC was associated with an elevated risk of CRC (odds ratios (OR) per unit SD increase = 1.46, 95% confidence interval [CI]: 1.20–1.79, p = 1.68 × 10−4). The pooled ORs for LDL, HDL, and TG were 1.05 (95% CI: 0.92–1.18, p = 0.49), 0.94 (95% CI: 0.84–1.05, p = 0.27), and 0.98 (95% CI: 0.85–1.12, p = 0.75) respectively. A genetic risk score for 3‐hydoxy‐3‐methylglutaryl‐coenzyme A reductase (HMGCR) to mimic the effects of statin therapy was associated with a reduced CRC risk (OR = 0.69, 95% CI: 0.49–0.99, p = 0.046). This study supports a causal relationship between higher levels of TC with CRC risk, and a further rationale for implementing public health strategies to reduce the prevalence of hyperlipidaemia.

764 Background: Psychosocial distress screening and assessment in patients with gastrointestinal (GI) cancers has an established importance due to the distress experienced during and post treatment. GI cancer patients receiving radiotherapy (RT) for curative or palliative measures were reviewed in order to determine if there was a relationship between patient reported distress (PRD) and survival. Methods: Patients at our institution who receive external beam RT for GI cancers completed a 30 question PRD survey that also included a linear analog measure of overall distress, the National Comprehensive Cancer Network (NCCN) Distress Thermometer, which ranged from 1 (low overall distress) to 10 (high overall stress) at the start of and/or during treatment. Each question on the PRD questionnaire concentrated on a possible cause of distress. It allowed patients to rate distress levels for each question from 1 to 5 (1 being the least distressed and 5 being the most distressed), and also overall distress according. The reported clinical results of the PRD questionnaire were retrospectively reviewed in patients receiving RT for GI cancers from Jan 2012 to Aug 2015. Patients were considered distressed if their overall PRD score was 5 or greater (PRD+) or not distressed (PRD-) if their score was 4 or under. Overall survival between PRD+ and PRD- was compared using the Kaplan-Meier method. Results: PRD surveys were completed by 134 consecutive patients, 67 (50%) male and 67 (50%) female within 30 days of starting RT. The median age was 65 years (range 28 to 93). The top histological finding was adenocarcinoma, 90 patients (60%). 113 (84%) received chemotherapy and 64 (48%) underwent surgery. 102 (75%) treatments were curative and 32 (25%) were palliative. Overall NCCN distress thermometer results ranged from 0 to 10, with a median of 4. Median follow-up was 2.7 years. Distressed patients (PRD+) had inferior survival to those not distressed (PRD-) at 2 years, 52% vs. 72%, p<0.02. Conclusions: Patient reported distress is associated with an inferior survival in patients receiving radiotherapy for gastrointestinal tumors.

677 Background: Napabucasin a first-in-class cancer stemness inhibitor in clinical development, suppresses cancer stemness by targeting Stat3-driven gene transcription. Preclinically, potent and broad-spectrum anti-cancer activity was observed in vitro and in vivo, alone and in combination with other agents. In a phase 1 study, napabucasin monotherapy was well tolerated with encouraging signs of anti-tumor activity at the RP2D of 500 mg BID. Methods: The current open-label, multi-center study includes phase II expansion in pts with refractory, K- Raswt mCRC to confirm safety and anti-tumor activity of napabucasin administered orally at 480mg BID in combination with panitumumab (6mg/kg bi-weekly). Results: 72 pts were enrolled, 48 pts were evaluable by RECIST of which 7 (15%) and 41 (85%) had 2 or >3 prior treatment lines, respectively. Of the 48 evaluable pts, 64.6% (31/48) were previously treated with an anti-EGFR agent. No new adverse events (AEs) were observed and most common AEs included grade 1/2 diarrhea, nausea, abdominal cramps, and vomiting. Among 48 pts enrolled who received RECIST evaluation, Disease Control Rate (DCR) was observed in 25 pts (52.1%) of which 3 pts achieved PR (6%) and 22 pts achieved SD (45%). Among 31 pts previously treated with anti-EGFR therapy, DCR was observed in 15 pts (48%) compared with DCR of 59% observed in 10 out of 17 anti-EGFR naïve pts receiving a scan. Conclusions: This phase II study confirmed that napabucasin can be safely combined with panitumumab at full dose and shows encouraging anti-tumor activity in pts with K- Ras wt mCRC, regardless of prior anti-EGFR exposure, suggesting that napabucasin may sensitize pts to repeat anti-EGFR therapy. Clinical trial information: NCT01776307. [Table: see text]

593 Background: Cancer stem cells or stemness-high cancer cells are considered to be fundamentally important for resistance to therapy, recurrence and metastasis. Napabucasin, a first-in-class cancer stemness inhibitor in clinical development, suppresses cancer stemness by targeting Stat3-driven gene transcription. Preclinical studies suggest that napabucasin sensitizes heterogeneous cancer cells to chemotherapeutics and targeted agents. Methods: This study was performed to assess signs of anti-tumor activity of napabucasin in combination with FOLFIRI +/- Bev in CRC pts. Napabucasin was administered at 240 mg BID. FOLFIRI (5-FU 400 mg/m2 bolus with 2400 mg/m2, irinotecan 180 mg/m2, and leucovorin 400 mg/m2 infusion) +/- Bev 5 mg/kg was administered biweekly until disease progression or other discontinuation criterion. pSTAT3 status of archival tumor tissue was assayed by immunohistochemistry using the H-score with pSTAT3highdefined as ≥ 5% pSTAT3+ cancer cells and tumor stroma staining at ≥ 2+ intensity. Results: 63 CRC pts with an average of >2 prior therapy lines were enrolled. No pharmacokinetic interactions or dose-limiting toxicity was observed. Most common adverse events (AEs) included grade 1/2 diarrhea, nausea, vomiting and fatigue. 25 pts had grade 3 AEs, including diarrhea (14), fatigue (4), dehydration (2), electrolyte imbalance (4), nausea (1) and weight loss (1) resolved with dose reduction and supportive care. Among 63 pts enrolled who received RECIST evaluation, disease control (CR+PR+SD) was observed in 49 pts (86%) with an overall response (CR+PR) of 28% with 1 pt achieving CR. Clinical trial information: NCT02024607. Conclusions: This phase Ib/II study suggests napabucasin may sensitize chemorefractory CRC to FOLFIRI +/- Bev. Encouraging signs of synergistic activity between napabucasin and FOLFIRI was observed in CRC pts regardless of pSTAT3 status.[Table: see text]

Background: Giant cell tumor (GCT) of bone is a benign, though locally aggressive tumor, classically described as an eccentric lytic lesion, often with cortical expansion and destruction. It typically involves the metaphysis or epiphysis of long bones in skeletally mature patients, with a slight female predominance. The incidence in the small bones of the hand has been reported to be 2% to 5%. Methods: Treatment options have evolved in recent years, and currently include intralesional curettage with or without adjuvant therapy, wide resection, and occasionally amputation. Results: In this report, we present a long-term follow-up (10 years) of a patient with GCT involving a metacarpal, who was initially reconstructed with a metacarpal head allograft, which was eventually revised to a metacarpophalangeal (MCP) total joint arthroplasty. Conclusions: To our knowledge, this is the only report of pyrocarbon being used for tumor reconstruction and the only report of late MCP allograft salvage.

Background Variable expressivity and incomplete penetrance between individuals with identical long QT syndrome (LQTS) causative mutations largely remain unexplained. Founder populations provide a unique opportunity to explore modifying genetic effects. We examined the role of a novel synonymous KCNQ1 p.L353L variant on the splicing of exon 8 and on heart rate corrected QT interval (QTc) in a population known to have a pathogenic LQTS type 1 (LQTS1) causative mutation, p.V205M, in KCNQ1-encoded Kv7.1. Methods 419 adults were genotyped for p.V205M, p.L353L and a previously described QTc modifier (KCNH2-p.K897T). Adjusted linear regression determined the effect of each variant on QTc, alone and in combination. In addition, peripheral blood RNA was extracted from three controls and three p.L353L-positive individuals. The mutant transcript levels were assessed via qPCR and normalised to overall KCNQ1 transcript levels to assess the effect on splicing. Results For women and men, respectively, p.L353L alone conferred a 10.0 (p=0.064) ms and 14.0 (p=0.014) ms increase in QTc and in men only a significant interaction effect in combination with the p.V205M (34.6 ms, p=0.003) resulting in a QTc of ∼500 ms. The mechanism of p.L353L's effect was attributed to approximately threefold increase in exon 8 exclusion resulting in ∼25% mutant transcripts of the total KCNQ1 transcript levels. Conclusions Our results provide the first evidence that synonymous variants outside the canonical splice sites in KCNQ1 can alter splicing and clinically impact phenotype. Through this mechanism, we identified that p.L353L can precipitate QT prolongation by itself and produce a clinically relevant interactive effect in conjunction with other LQTS variants.