The molecular landscape of <i>PIWIL1</i> expression in colorectal adenocarcinoma (CRC).
Authors: Tony Varughese, Yasmine Baca, Lishann Ingram, Gretchen Hubbard, Joanne Xiu, Emil Lou, Hiroyuki Arai, Anthony F. Shields, Moh'd M. Khushman, Francesca Battaglin, Jimmy J. Hwang, Richard M. Goldberg, Andreas Seeber, Heinz-Josef Lenz, Sanjay Goel, John Marshall, Matthew James Oberley, Benjamin Adam Weinberg
Journal: Journal of Clinical Oncology (2024)

3546 Background: PIWIL1 is a cancer testis antigen overexpressed in solid tumors, particularly CRC, and is associated with advanced stage and poor prognosis. It is potentially a new therapeutic target as PIWIL1 is not expressed in adult somatic tissue. A novel T cell receptor/PIWIL1 bispecific antibody is in development, restricted to individuals with human leukocyte antigen (HLA) A-02. We sought to characterize the molecular landscape of PIWIL1 in CRC. Methods: 26,581 CRC tumors were tested by next-generation sequencing (NGS) on DNA (592-gene or whole exome [WES]) and RNA (whole transcriptome [WTS]) at Caris Life Sciences (Phoenix, AZ). dMMR/MSI-H was tested by immunohistochemistry (IHC) and NGS, HLA genotypes by WES and PD-L1 by IHC (SP142, 2+, 5%). Tumor mutational burden (TMB) high was defined as ≥ 10 mt/Mb. RNA expression was used to estimate the tumor microenvironment using QuantiSEQ and RNA signatures (interferon gamma [IFNγ]; T-cell inflamed [TIS]) predictive of immune checkpoint blockade (IO) response. The top (H) and bottom (L) quartiles of PIWIL1 expression were compared using Chi-square/Fisher-Exact, and significance was determined as p adjusted for multiple comparisons (Q&lt;0.05). Real-world overall survival (rwOS) was obtained from insurance claims and calculated from tissue collection to last contact. Results: Patients with PIWIL1-H were older (median age 65 v 61, Q&lt;0.01) and more likely to be female (50.8% v 41.3%, Q&lt;0.01), compared to PIWIL1-L. PIWIL1 median expression was higher in right- v left-sided primary tumors (2.0 v 1.3 transcripts per million [TPM], Q&lt;0.05). No significant difference in PIWIL1 expression was observed among HLA genotypes. dMMR/MSI-H, TMB-H and PD-L1+ were higher in PIWIL1-H v PIWIL1-L (13.9% v 6.5%, 17.6% v 10.4%, 6.4% v 3.4%, all Q&lt;0.05). IO-related gene expression ( LAG3, IDO1, CTLA4 and others) were positively associated with PIWIL1 expression (fold change [FC]: 1.4-2.7, Q&lt;0.05). High IFNγ and TIS were associated with PIWIL1-H (Q&lt;0.001). PIWIL1 expression showed a positive association with infiltration of neutrophils, monocytes, CD4+T, dendritic and NK cells (FC: 1.3-2.9, Q&lt;0.05) while Tregs and M1 macrophages had a negative association (0.8-0.9, Q&lt;0.05). In pMMR/MSS CRC, KRAS, BRAF and TP53 mutations and loss of heterozygosity were higher in PIWIL1-H v PIWIL1-L (81% v 69%, 53% v 41%, 16% v 3%, 14% v 10%, all Q&lt;0.05) but not for PIK3CAmutations (14% v 17%). For rwOS, PIWIL1-H had longer median OS than PIWIL1-L, 31.2 v 28.8 months (HR 0.95; 95% CI 0.90-0.99, p=0.043). There was no significant rwOS difference observed in IO-treated tumors. Conclusions: PIWIL1-H CRC is associated with higher rates of dMMR/MSI-H, TMB-H and PD-L1+ as well as IO-related gene expression and signatures that are predictive of response to IO. These data suggest the PIWIL1-H subpopulation could potentially derive substantial benefit from PIWIL1-targeted immunotherapy which should be evaluated in clinical trials.