Abstract
Uterine smooth muscle tumours of uncertain malignant potential (STUMP) are diagnostically and clinically challenging. A mean to distinguish benign STUMP (leiomyoma) from malignant STUMP (leiomyosarcoma) is required. Chronic cellular proliferation is an important aspect of malignant cells. In the normal cell, telomeres that protect chromosome ends experience attrition at each cell division until a critical length occurs and cell division ceases. Cancerous cells maintain telomeres (telomere maintenance) by activating a telomere maintenance mechanism either telomerase activity or a less well characterised mechanism that is recombination based, known as the alternative lengthening of telomeres (ALT).
Recent progress in the molecular subtyping of mesenchymal tumours has identified prognostic implications in the type of telomere maintenance mechanism employed, wherein patients with ALT positive tumours have a worse prognosis compared to those with telomerase activation. This study aimed to identify if ALT or mutations associated with ALT positive tumours were prognostic markers in uterine sarcoma, and whether these markers could identify STUMP with a malignant behavior. Seventy-one uterine tumours from Hong Kong and New Zealand were examined. The tumours comprised of uterine leiomyoma (LM, n = 11), leiomyosarcoma (LMS, n = 43) and STUMP (n = 17). Tissue sections were stained for a hallmark of the ALT mechanism (ALT-associated promyelocytic leukaemia protein (PML) bodies, APBs), which are co-localised PML and telomere DNA aggregates in cell nuclei. In this study APBs were measured using immunofluorescence detect PML and fluorescent in situ hybridisation to detect telomeric DNA and con-focal microscopy. Tissue sections were also stained for two molecular variants associated with ALT positive tumours, tumour protein 53 (p53), and the R132H mutation in isocitrate dehydrogenase 1 (IDH 1) using immunohistochemistry. Antibodies specifically raised against the R132H IDH 1 mutation and to full-length p53 were used.
Strong immunohistochemical expression for p53 (a surrogate for p53 mutation) was found in 41.9% of LMS, 29.4% of STUMP, and was absent in LM. APBs were present in 39.5% of STUMP, 23.5% of LMS, and was absent in LM. The R132H IDH 1 mutation was observed in 14% of LMS, 5.9% of STUMP, and 18.2% of LM. P53 immunohistochemical expression was the only molecular variant associated with a poor patient prognosis in LMS and STUMP (P = 0.007). No association with survival was found for LMS and STUMP patients, as a combined group, with APB, or R132H IDH 1 positive tumours (P = 0.36, P = 0.89, respectively). However APB determination identified 4/6 of the 17 STUMP cases that resulted in a poor prognosis.
This is the largest study to date examining ALT maintenance molecular markers with survival time in smooth muscle tumours of uncertain malignant potential in the uterus.
Our results conclusively demonstrated p53 as a viable prognostic marker found in STUMP and leiomyosarcoma. Although APB and R132H IDH 1 mutation do not hold the same prognostic value, they were found in all tumour types; with the exception of APB in leiomyoma. We conclude that ALT TMM requires further investigation and is a potential marker of poor prognosis. Immunohistochemical expression of p53 is confirmed as identifying STUMP with a poor outcome.