Background We have previously shown that a possible complementary target to PD1-based immune-checkpoint blockade (ICB) is the adhesion molecule CD155, which promotes tumor growth and metastasis in mouse models. To date, it is unclear to what extent tumor CD155 expression impacts the immune infiltrate contexture or if expression of CD155 by human tumors affects sensitivity to ICB. Methods We assessed pretreatment tumor FFPE specimens from 146 metastatic melanomas patients treated with immune checkpoint blockade (ICB) and 41 patients that have received 1st line BRAF/MEK targeted therapy and no ICB. CD155 expression was defined by immunohistochemistry (IHC) H-score. The immune infiltrate was separately analysed in stroma and parenchymal (intratumor) regions using multiplex immunohistofluorescence (IHF) for CD8, PD1 and SOX10. Associations were made between IHC analyses, bulk tumor RNA-seq results, and immunotherapeutic response (RECIST, PFS, and disease specific OS). Key findings were functionally validated in a relevant mouse melanoma model. Results Melanoma patients with high levels of tumor CD155 (score 3+) frequently had progressive disease or shorter PFS through promotion of dysfunctional PD1+CD8+ T cells. Further, the intratumor ratio of PD1+CD8+ to total CD8+ T cells (PD1tR) is a strong predictor of ICB refractory patients. Importantly, outcome correlations appeared specific to ICB therapy and were not present in melanoma patients treated with BRAF/MEK targeted therapy. In humans, CD155 high tumors show reduced Interferon-gamma and cytotoxic gene signatures. In PD1 resistant mouse tumor models, deletion of CD155 prevented accumulation of intratumor PD1hiCD8+ T cells. Additionally, therapeutic blockade of the CD155 cognate receptors TIGIT and CD96 restored IFNγ production and improved anti-PD1 tumor control. Conclusion Our findings are the first to demonstrate that tumor CD155 underpins the accumulation of dysfunctional PD1hiCD8+ T cells in human tumors and propose pretreatment PD1tR as a potential biomarker of response to ICB. Legal entity responsible for the study The Council of the Queensland Institute of Medical Research. Funding Bristol-Myers Squibb. Disclosure P.A. Ascierto: Advisory / Consultancy, Research grant / Funding (institution): Bristol-Myers Squibb; Advisory / Consultancy, Research grant / Funding (self): Roche-Genentech; Advisory / Consultancy, Research grant / Funding (self): Array; Advisory / Consultancy, Travel / Accommodation / Expenses: MSD; Advisory / Consultancy: Novartis; Advisory / Consultancy: Merck Serono; Advisory / Consultancy: Pierre Fabre; Advisory / Consultancy: Incyte; Advisory / Consultancy: Genmab; Advisory / Consultancy: Newlink Genetics; Advisory / Consultancy: Medimmune; Advisory / Consultancy: AstraZeneca; Advisory / Consultancy: Syndax; Advisory / Consultancy: Sun Pharma; Advisory / Consultancy: Sanofi; Advisory / Consultancy: Idera; Advisory / Consultancy: Ultimovacs; Advisory / Consultancy: Sandoz; Advisory / Consultancy: Immunocore. G. V. Long: Advisory / Consultancy: Aduro; Advisory / Consultancy: Amgen; Advisory / Consultancy: Bristol-Myers Squibb; Advisory / Consultancy: Merck MSD; Advisory / Consultancy: Novartis; Advisory / Consultancy: Roche. R. A. Scolyer: Advisory / Consultancy: Merck Sharp Dohme; Advisory / Consultancy: Novartis; Advisory / Consultancy: Myriad; Advisory / Consultancy: NeraCare. W. C. Dougall: Research grant / Funding (self): Bristol-Myers Squibb; Advisory / Consultancy: Omeros Corporation ; Advisory / Consultancy: Cascadia Drug Development Group. M. W. L. Teng: Speaker Bureau / Expert testimony: Roche; Speaker Bureau / Expert testimony: MSD; Speaker Bureau / Expert testimony: Bristol-Myers Squibb. M. Smyth: Research grant / Funding (self): Bristol-Myers Squibb; Research grant / Funding (self): Aduro Biotech; Research grant / Funding (self): Tizona Pharmaceuticals. All other authors have declared no conflicts of interest.

Background: Despite the great success of anti-PD-1 therapy (Pembrolizumab or Nivolumab), resistance is still an issue. Resistance may be caused by activation of additional immune evasive mechanisms by the tumour cells and the establishment of an immunosuppressive tumour microenvironment through the action of innate immune cells. One known mechanism of immune evasion from CD8+ T cells is the downregulation of MHC class I molecules on tumour cells leading to down-regulation of antigen presentation. Natural Killer (NK) cells, that form part of the innate immune system, actively seek out cells that downregulate MHC class I.

Background: Survival outcomes for advanced stage metastatic melanoma patients have significantly improved following treatment with combined CTLA-4 and PD-1 checkpoint inhibitors. Although some patients have demonstrated durable responses to immunotherapy, others derive minimal or no benefit. Phenotyping and characterising the immune cells present within and surrounding the tumour may predict response to immunotherapy and improve our understanding of the mechanisms driving differences in response between patients.

We report four previously undescribed families with germline BRCA1-associated protein-1 gene (BAP1) mutations and expand the clinical phenotype of this tumor syndrome. The tumor spectrum in these families is predominantly uveal malignant melanoma (UMM), cutaneous malignant melanoma (CMM) and mesothelioma, as previously reported for germline BAP1 mutations. However, mutation carriers from three new families, and one previously reported family, developed basal cell carcinoma (BCC), thus suggesting inclusion of BCC in the phenotypic spectrum of the BAP1 tumor syndrome. This notion is supported by the finding of loss of BAP1 protein expression by immunochemistry in two BCCs from individuals with germline BAP1 mutations and no loss of BAP1 staining in 53 of sporadic BCCs consistent with somatic mutations and loss of heterozygosity of the gene in the BCCs occurring in mutation carriers. Lastly, we identify the first reported recurrent mutation in BAP1 (p.R60X), which occurred in three families from two different continents. In two of the families, the mutation was inherited from a common founder but it arose independently in the third family.

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype lacking expression of estrogen and progesterone receptors (ER/PR) and HER2, thus limiting therapy options. We hypothesized that meta-analysis of TNBC gene expression profiles would illuminate mechanisms underlying the aggressive nature of this disease and identify therapeutic targets. Meta-analysis in the Oncomine database identified 206 genes that were recurrently deregulated in TNBC compared with non-TNBC and in tumors that metastasized or led to death within 5 years. This 'aggressiveness gene list' was enriched for two core functions/metagenes: chromosomal instability (CIN) and ER signaling metagenes. We calculated an 'aggressiveness score' as the ratio of the CIN metagene to the ER metagene, which identified aggressive tumors in breast cancer data sets regardless of subtype or other clinico-pathological indicators. A score calculated from six genes from the CIN metagene and two genes from the ER metagene recapitulated the aggressiveness score. By multivariate survival analysis, we show that our aggressiveness scores (from 206 genes or the 8 representative genes) outperformed several published prognostic signatures. Small interfering RNA screen revealed that the CIN metagene holds therapeutic targets against TNBC. Particularly, the inhibition of TTK significantly reduced the survival of TNBC cells and synergized with docetaxel in vitro. Importantly, mitosis-independent expression of TTK protein was associated with aggressive subgroups, poor survival and further stratified outcome within grade 3, lymph node-positive, HER2-positive and TNBC patients. In conclusion, we identified the core components of CIN and ER metagenes that identify aggressive breast tumors and have therapeutic potential in TNBC and aggressive breast tumors. Prognostication from these metagenes at the mRNA level was limited to ER-positive tumors. However, we provide evidence that mitosis-independent expression of TTK protein was prognostic in TNBC and other aggressive breast cancer subgroups, suggesting that protection of CIN/aneuploidy drives aggressiveness and treatment resistance.

Veronique Ouellet (ouelletv@yahoo.ca) Tak Hay Ling (takhay7777@yahoo.ca) Karine Normandin (ka_normandin@hotmail.com) Jason Madore (jason.madore@gmail.com) Christian Lussier (clu2001@videotron.ca) Veronique Barres (veronique.barres@usherbrooke.ca) Dimcho Bachvarov (dimtcho.batchvarov@crhdq.ulaval.ca) Claudine Rancourt (claudine.rancourt@usherbrooke.ca) Patricia N Tonin (patricia.tonin@mcgill.ca) Diane M Provencher (diane.provencher.chum@ssss.gouv.qc.ca) Anne-Marie Mes-Masson (anne-marie.mes-masson@umontreal.ca)

10096 Background: The nuclear accumulation of growth factor receptor was reported to be associated to increased cell proliferation. Cyclin D1 and Ki67 are nuclear markers of cell proliferation. Deregulation of Cyclin D1 and Ki67 expression play a role in tumorigenesis and metastasis. Recently, we observed that nuclear localization of ErbB3 was associated with prostate cancer progression. The objective of this study was to determine if the association of cell proliferation markers and nuclear localization of ErbB3 could predict biochemical recurrence (BCR) in patients with prostate cancer following radical prostatectomy. Methods: Using immunohistochemistry we analyzed a tissue microarray containing 386 cores from 64 formalin-fixed paraffin embedded specimens from prostate cancer patients who had undergone radical prostatectomy. No patient had received hormone therapy prior to surgery and prior to BCR. Antibodies against Cyclin D1, ErbB3 and Ki67 proteins were used. Results: Nuclear staining was 60%, 67% and 86% for Cyclin D1, ErbB3 and Ki67 respectively. In our cohort, 29 of 64 PCa patients (45%) had a BCR after a median 3 years of follow-up. Thirty seven (37) percent of patients had positive nuclear staining for all three markers. BCR free survival probability at 3 years was not significant for each marker individually, except for ErbB3 in positive surgical margin patients. When all three markers were combined for nuclear staining Kaplan-Meier analysis BCR free was 0.4 and 0.1 for positive and negative nuclear staining respectively (p=0.0068). Univariate COX regression analysis shows a 2.98 fold (95% CI: 1.29 - 6.86, p=0.01) higher rate of BCR in patients positive for these three markers. In addition, in a multivariate model, including pre-operative PSA (p=0.19), pathologic stage (p=0.29), Gleason grade (p=0.40) and specimens that had positive nuclear staining for the 3 markers were associated with a 3.97 fold higher rate of BCR (95% CI: 1.54 - 10.25, p=0.0068). Conclusion: These results suggest that the association of cell proliferation markers and nuclear localization of ErbB3 could be useful in predicting recurrence following radical prostatectomy and guide therapeutic decisions. Large scale trials are needed to confirm these results. No significant financial relationships to disclose.

In order to elucidate the biological variance between normal ovarian surface epithelial (NOSE) and epithelial ovarian cancer (EOC) cells, and to build a molecular classifier to discover new markers distinguishing these cells, we analysed gene expression patterns of 65 primary cultures of these tissues by oligonucleotide microarray. Unsupervised clustering highlights three subgroups of tumours: low malignant potential tumours, invasive solid tumours and tumour cells derived from ascites. We selected 18 genes with expression profiles that enable the distinction of NOSE from these three groups of EOC with 92% accuracy. Validation using an independent published data set derived from tissues or primary cultures confirmed a high accuracy (87–96%). The distinctive expression pattern of a subset of genes was validated by quantitative reverse transcription–PCR. An ovarian-specific tissue array representing tissues from NOSE and EOC samples of various subtypes and grades was used to further assess the protein expression patterns of two differentially expressed genes (Msln and BMP-2) by immunohistochemistry. This study highlights the relevance of using primary cultures of epithelial ovarian cells as a model system for gene profiling studies and demonstrates that the statistical analysis of gene expression profiling is a useful approach for selecting novel molecular tumour markers.

We used an oligonucleotide-based DNA microarray to identify potential markers in 39 primary cultures of ovarian cancer specimens compared with 11 primary cultures of normal ovarian epithelia. Differential gene expression of IL-18 and FGF-2 was validated on a subset of samples by quantitative PCR and by IHC, using an independent tissue array of 90 cores of 20 normal ovarian surface epithelia and 70 EOCs representing different grades and pathologies of ovarian disease. We further compared, by ELISA, these two markers with CA125 in sera from 25 cancer-free and 47 ovarian cancer patients. IL-18 and FGF-2 proteins were significantly elevated in tumor tissues (p<0.04) and sera (p<0.05) from patients with ovarian cancer. In combination, the three markers (IL-18, FGF-2, and CA125) showed similar sensitivity in scoring for ovarian cancer (35/45 patients) compared to that of CA125 alone (37/45) and significantly improved the specificity of detection (20/25 patients) compared to each marker individually (15/25 for CA125; 18/25 FGF-2; 16/25 for IL-18). In conclusion we show that a combination of the three serum markers (IL-18, FGF-2 and CA125) is associated with EOC, with higher specificity than CA125 alone. Prospective studies with a large cohort of susceptible ovarian cancer patients will be required to expand these findings.