Relationships between highly recurrent tumor suppressor alterations in 489 leiomyosarcomas

Background Leiomyosarcoma (LMS) is the most common soft tissue and uterine sarcoma, but no standard therapy is available for recurrent or metastatic LMS. TP53, p16/RB1, and PI3K/mTOR pathway dysregulations are recurrent events, and some LMS express estrogen receptor (ER) and/or progesterone receptor (PR). To characterize relationships between these pathway perturbations, the authors evaluated protein expression in soft tissue and uterine nonprimary leiomyosarcoma (np‐LMS), including local recurrences and distant metastases. Methods TP53, RB1, p16, and PTEN expression aberrations were determined by immunohistochemistry (IHC) in tissue microarrays (TMAs) from 227 np‐LMS and a comparison group of 262 primary leiomyosarcomas (p‐LMS). Thirty‐five of the np‐LMS had a matched p‐LMS specimen in the TMAs. Correlative studies included differentiation scoring, ER and PR IHC, and CDKN2A/p16 fluorescence in situ hybridization. Results Dysregulation of TP53, p16/RB1, and PTEN was demonstrated in 90%, 95%, and 41% of np‐LMS, respectively. PTEN inactivation was more common in soft tissue np‐LMS than uterine np‐LMS (55% vs 31%; P = .0005). Moderate‐strong ER expression was more common in uterine np‐LMS than soft tissue np‐LMS (50% vs 7%; P < .0001). Co‐inactivation of TP53 and RB1 was found in 81% of np‐LMS and was common in both soft tissue and uterine np‐LMS (90% and 74%, respectively). RB1, p16, and PTEN aberrations were nearly always conserved in p‐LMS and np‐LMS from the same patients. Conclusions These studies show that nearly all np‐LMS have TP53 and/or RB1 aberrations. Therefore, therapies targeting cell cycle and DNA damage checkpoint vulnerabilities should be prioritized for evaluations in LMS. Aberrations of TP53, p16/RB1, and PTEN are found in 90%, 95%, and 41% of metastatic soft tissue and uterine leiomyosarcomas, respectively, with PTEN inactivation being more common in soft tissue cases. These key aberrations are generally conserved between primary and metastatic disease in a given patient.