Expression of Thymidylate Synthase in Cancer: A Tissue Microarray Study Involving 17,371 Cancers from 136 Tumor Entities

Background/Objectives: Thymidylate synthase (TYMS) represents an important therapeutic target. Methods: In this study, TYMS expression was analyzed by immunohistochemistry on a tissue microarray containing 17,371 samples from 136 different tumor types. Results: TYMS staining was seen in 42.9% of 15,361 analyzable tumors, with weak staining in 35.4%, moderate in 5.7%, and strong in 1.8%. TYMS occurred in at least one case of 127 categories, of which 71 showed TYMS staining in at least 50% of cases, and 56 included at least one case with strong positivity. TYMS positivity occurred most commonly in lymphomas (81.3–96.5%), sarcomas and sarcomatoid carcinomas (33.3–100%), malignant melanoma (70.5–90.7%), cervical adenocarcinoma (78.3%), and squamous cell carcinomas of various sites (57.1–77.9%). High TYMS expression was linked to advanced pT (p = 0.0097), high grade (p < 0.0001), ER negativity (p < 0.0001), and PR negativity (p = 0.0002) in invasive breast cancer of no special type; high grade (p < 0.0050), high UICC stage (p = 0.0060), and nodal metastasis (p = 0.0120) in clear cell renal cell carcinoma (RCC); high grade (p < 0.05) and nodal metastasis (p = 0.0045) in papillary RCC; high Gleason grade (p < 0.0001) and advanced pT stage (p = 0.0149) in prostatic adenocarcinoma; high pT (p < 0.0001), nodal metastasis (p = 0.005), lymphatic (p = 0.0064) and venous invasion (p = 0.0005), left side location (p < 0.0001), and microsatellite instability (p < 0.0001) in colorectal adenocarcinoma; and high grade (p < 0.0001) in squamous cell carcinomas of different sites. Conclusions: TYMS is often overexpressed across different cancer entities and shows associations with several adverse histopathological parameters commonly used to describe tumor phenotypes.