Abstract 1205: Inferring allele-specific copy number aberrations and tumor phylogeography from spatially resolved transcriptomics

Abstract Tumors evolve through the acquisition of somatic mutations over time and across space. While the temporal aspects of tumor evolution can be inferred by applying phylogenetic techniques to bulk or single-cell DNA sequencing data, the spatial aspects of tumor evolution remain understudied. Spatially resolved transcriptomics (SRT) measures gene expression at thousands of spatial locations in a tumor, but does not directly measure genetic aberrations. Thus, SRT data has not yet been fully utilized for tumor evolution studies. We introduce CalicoST, an algorithm that simultaneously infers allele-specific copy number aberrations (CNAs) and derives a phylogeographic model of tumor evolution from SRT data. By modeling CNA-induced perturbations in both gene expression and allele frequencies, CalicoST identifies important types of CNAs - including copy-neutral loss of heterozygosity (CNLOH) and mirrored subclonal CNAs - that are invisible to total copy number analysis. On SRT data from nine patients from the Human Tumor Atlas Network (HTAN), CalicoST achieves an average accuracy of 86%, approximately 21% higher than existing methods. On two of these patients with multiple adjacent slices, CalicoST reconstructs a tumor phylogeography that describes the spread of cancerous clones in three-dimensional space. CalicoST analysis of multiple SRT slices from a cancerous prostate organ reveals five spatially coherent clones, with mirrored subclonal CNAs distinguishing clones on the two sides of the prostate, and a bifurcating phylogeography in both genetic and physical space that suggests a polyclonal cancer. Citation Format: Cong Ma, Metin Balaban, Jingxian Liu, Siqi Chen, Li Ding, Benjamin J. Raphael. Inferring allele-specific copy number aberrations and tumor phylogeography from spatially resolved transcriptomics abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1205.