Genetic and clinico-pathologic analysis of metastatic uveal melanoma

Abstract

Uveal melanoma is the most common malignant tumor of the adult eye. Fifty percent of tumors will eventually metastasize, and there are no effective treatments for them. Recent studies of uveal melanoma have identified activating mutations in GNAQ and GNA11, loss-of-function mutations in the tumor suppressor gene BAP1, and recurrent mutations in codon 625 of SF3B1. Previous studies have reported the existence of a higher frequency of GNA11 than GNAQ mutations, frequent BAP1 loss, and rare SF3B1 mutations in metastatic uveal melanoma. We analyzed a cohort of 30 uveal melanoma metastases for the occurrence of GNAQ, GNA11, and SF3B1 mutations, as well as BAP1 loss, and correlated these parameters with clinical and histopathologic features. Most (92%) tumors were composed of cells with an epithelioid or mixed (o100% spindle cells) morphology. Tumor samples composed exclusively of spindle cells were rare (n ¼ 2, 8%). Most tumors showed a moderate to marked degree of nuclear pleomorphism (n ¼ 24, 96%), and contained hyperchromatic, vesicular nuclei with variably conspicuous nucleoli. GNA11 mutations were considerably more frequent than GNAQ mutations (GNA11, GNAQ, and wild-type in 18 (60%), 6 (20%), and 6 (20%) cases, respectively). SF3B1 mutation was found in 1 of 26 tumors (4%), whereas loss of BAP1 expression was present in 13 of 16 tumors (81%). Patients with GNA11-mutant tumors had poorer disease-specific survival (60.0 vs 121.4 months, P ¼ 0.03) and overall survival (50.6 vs 121.4 months, P ¼ 0.03) than those with tumors lacking GNA11 mutations. The survival data, combined with the predominance of GNA11 mutations in metastases, raises the possibility that GNA11-mutant tumors may be associated with a higher risk of metastasis and poorer prognosis than GNAQ-mutant tumors. Further studies of uveal melanoma are required to investigate the functional and prognostic relevance of oncogenic mutations in GNA11 and GNAQ.

Rare SF3B1 R625 mutations in cutaneous melanoma

“…This is in contrast to previous finding that SF3B1 R625 mutations are rare in metastatic tumors and are associated with better prognosis [2, 4, 7]. Harbour et al did not detect any SF3B1 mutation in their five distant metastatic uveal melanoma [2], and Griewank et a l found one out of 26 metastatic uveal melanoma samples [7]. The difference might be due to sample bias, since there are more metastatic than primary tumors in our cohort.…”

Uveal Melanoma Nuclear BRCA1-Associated Protein-1 Immunoreactivity Is an Indicator of Metastasis

“…Another investigation found a mutation frequency of 45% (29/64) for BAP1 in unselected cases using exome and Sanger sequencing 8 . Whole-exome sequencing of metastatic uveal melanoma identified inactivating somatic mutations in BAP1 in 81-84% of metastatic tumors 10 , 16 . Ewens et al reported that 77% of uveal melanomas carrying BAP1 mutations developed metastasis 17 .…”

The biology of uveal melanoma

“…The proportion of spindle cell histology is more frequent in younger patients and has decreased over time [10], probably as a consequence of increased age at diagnosis. Accordingly, metastatic UM shows prevalently epithelioid cells although a component of spindle-like cells is always present [126]. Other histopathological features commonly used for assessing the malignant potential of UM are the number of mitotic figures and the presence of extracellular matrix periodic acid–Schiff-positive closed loops.…”

“…Many studies report mutation frequencies that are summarized in Table 3 [27, 28, 30, 32, 35, 83, 126, 128, 130, 147, 148, 157–172]. Initially, BRAF mutations had also been described for UM [173, 174] but these reports have not been confirmed.…”