Anaplastic transformation in thyroid cancer revealed by single cell transcriptomics.

The deadliest anaplastic thyroid cancer (ATC) often transforms from indolent differentiated thyroid cancer (DTC); however, the complex intra-tumor transformation process is poorly understood. We investigated an anaplastic transformation model by dissecting both cell lineage and cell fate transitions using single cell transcriptomes and genetic alteration data from patients with different subtypes of thyroid cancer. The resulting spectrum of ATC transformation included stress-responsive DTC cells, inflammatory ATC cells (iATCs), mitotic-defective ATC cells and extended all the way to mesenchymal ATC cells (mATCs). Further, our analysis identified two important milestones: 1) a diploid stage, where iATC cells were diploids with inflammatory phenotypes, and 2) an aneuploid stage, where mATCs gained aneuploid genomes and mesenchymal phenotypes producing excessive collagens and collagen-interacting receptors. In parallel, cancer-associated-fibroblasts showed strong interactions among mesenchymal cell-types, macrophages shifted from M1 to M2 states, and T cells reprogrammed from cytotoxic to exhausted states, highlighting new therapeutic opportunities for ATC.