A Subset of Serous Tubal Intraepithelial Carcinoma (STIC)-Like Lesions and Concurrent High-Grade Endometrial Carcinoma Are Genomically Related Entities.

In patients with high-grade endometrial carcinoma (HG-EC), concurrent isolated serous tubal intraepithelial carcinoma (STIC) or STIC-like lesions (STIC-LLs) in the fallopian tube(s) may be found. We sought to determine whether concurrently diagnosed HG-ECs and STIC-LLs are genetically related. Six HG-ECs, including serous carcinomas (n = 4) and carcinosarcomas with serous epithelial component (n = 2), with cooccurring STIC-LLs were identified and subjected to microdissection, DNA extraction, and panel sequencing targeting 468 cancer-related genes or, if DNA quantities were limited, to Sanger sequencing. WT1 and p53 protein expression was assessed by immunohistochemistry. We found that 3 HG-ECs and concurrent STIC-LLs shared pathogenic mutations, such as TP53 hotspot, NF2, FBXW7, and PIK3CA mutations. Immunohistochemical analysis revealed that the HG-EC of case 5 lacked WT1 expression and had aberrant p53 expression, although the matched STIC-LL displayed diffuse WT1 expression. Of the remaining 3 cases that did not show evidence of genetic relatedness based on the targeted sequencing panel, 1 STIC-LL harbored a clonal TP53 missense mutation, whereas the matched HG-EC had a distinct clonal TP53 hotspot mutation, a clonal FBXW7 hotspot mutation, and ERBB2 amplification. At the protein level, the p53 expression patterns of the HG-ECs and STIC-LLs were concordant in these 3 cases. Here, we demonstrate that cooccurring HG-ECs and STIC-LLs are genetically related in a subset of cases.