DNA ploidy and S-phase fraction as prognostic factors in patients with uveal melanomas

The genetics of uveal melanoma: an emerging framework for targeted therapy

Uveal melanoma is the second most common form of melanoma and the most common primary intraocular malignancy. Until recently, very little was known about the genetics of this aggressive cancer. Mutations in oncogenes and tumor suppressors that are common in other cancers are conspicuously absent in uveal melanoma. In recent years, however, uveal melanoma has begun to yield its secrets, and a fascinating picture is emerging of how it develops and progresses. Mutations in the G(q) alpha subunits, encoded by GNAQ and GNA11, appear to be early or perhaps initiating events that require further mutations for malignant transformation. On the other hand, mutations in the BRCA1-associated protein-1 (BAP1) appear to occur later and demarcate a molecular brink beyond which metastasis becomes highly likely. BAP1 mutations can also occur in the germline, leading to a distinctive cancer predisposition syndrome. These mutations appear to be key events that provide the potential for targeted therapy. This article will review the genetic findings in uveal melanoma over the past two decades and suggest important areas for future work.

A comparative transcriptomic analysis of uveal melanoma and normal uveal melanocyte

Background

Uveal melanoma is the most common primary intraocular tumor in adults in western countries. It is associated with very severe visual morbidity and may lead to distant metastases even after successful treatment of the primary tumor. In order to gain better insight into molecular mechanisms related to tumorigenesis and metastasis of uveal melanoma, we used next-generation sequencing technology (SOLiD, Life Technologies) to acquire global transcriptome alteration between posterior uveal melanoma cells and normal uveal melanocyte.

Results

From mRNAs of the cultured uveal melanoma cells and normal uveal melanocytes, we annotated more than 3.7×10⁷ and 2.7×10⁷ sequencing tags based on human Ensembl databases, respectively. For detailed analysis, we chose 5155 well-annotated genes mainly involved in the MAPK signaling pathway, cell cycle, cell adhesion junction, apoptosis, and P53 signaling pathways as well as melanogenesis. In an effort to confirm the authenticity of our sequencing results, we validated twenty-one identically differentially expressed genes by using quantitative real time PCR from cultured cell lines of other posterior uveal melanoma cells and normal uveal melanocytes.

Conclusion

We have identified a large number of potentially interesting genes for biological investigation of uveal melanoma. The expression profiling also provides useful resources for other functional genomic and transcriptome studies. These 21 potential genes could discriminate between uveal melanoma cells and normal uveal melanocyte, which may be indicative of tumorigenesis process. Our results further suggest that high-throughput sequencing technology provides a powerful tool to study mechanisms of tumogenesis in the molecular level.

Genomic Investigations of Posterior Uveal Melanoma

The specific genetic mechanisms responsible for the malignant behavior of uveal melanoma are not known. Unlike cutaneous melanoma, epidemiologic studies have not demonstrated a definitive germline form of uveal melanoma, though familial melanoma and racial predilections occur. Molecular cytogenetic characterization of uveal melanoma suggests that somatic deletions of chromosome 3 are associated with a worse prognosis. Microarray technology has been used to characterize uveal melanoma gene expression and may provide tests useful for determining prognosis. As an improved understanding of the cellular mechanisms used by uveal melanoma is gained, new opportunities to adapt or design therapeutic approaches may emerge.

Effects of proton beam irradiation on uveal melanomas: a comparative study of Ki-67 expression in irradiated versus non-irradiated melanomas

AIMS

To assess the cellular proliferation using the monoclonal antibody Ki-67, in paraffin embedded uveal melanomas irradiated by proton beam, as well as in non-irradiated uveal melanomas.

METHODS

30 enucleated eyes were included for histopathological study and Ki-67 immunostaining. Patients were enucleated between 1991 and 1996 for uveal melanoma, 14 after proton beam irradiation and 16 without treatment (control group). The mean follow up period was 2.5 years after diagnosis and 1 year after enucleation.

RESULTS

A significant relation was found between Ki-67 score and mitotic index (r = 0.56, p = 0.001), histological largest tumour diameter (r = 0.38, p = 0. 03), fibrosis (r = -0.35, p = 0.05), absence of tumoral pigmentation (p = 0.05), and presence of vascular thrombosis (p = 0.03). The Ki-67 score was significantly higher in the non-irradiated group (p = 0.01) and in the group of patients whose cause of enucleation was tumoral evolution (p = 0.005) compared with the group of patients enucleated after neovascular glaucoma. The Ki-67 score was very high in a case of orbital recurrence of uveal melanoma and metastatic death. 70% of metastasised tumours showed a Ki-67 score higher than the median value.

CONCLUSION

Ki-67 labelling is a reliable method of estimating the proliferative activity in uveal melanomas after proton beam irradiation. The Ki-67 score is significantly correlated with prognostic variables (mitotic index and histological largest tumour diameter), and with radiation effects after proton beam irradiation.

Histopathologic characteristics of uveal melanomas in eyes enucleated from the Collaborative Ocular Melanoma Study. COMS report no. 6

PURPOSE

To describe the principal histopathologic findings in a series of 1,527 globes with uveal melanoma and the relationship of these findings to each other.

METHODS

All eyes enucleated in the Collaborative Ocular Melanoma Study (COMS) were examined independently by three ophthalmic pathologists and the findings recorded on a data form. A composite of findings was obtained after adjudication.

RESULTS

The diagnosis was choroidal melanoma in 1,527 (99.7%) of 1,532 cases examined. Misdiagnoses were metastatic adenocarcinoma (four) and hemangioma (one). Spindle cell (9.0%), mixed cell (86.0%), and epithelioid cell (5.0%) types were observed. Medium tumors were located more posteriorly than large tumors. Considerable local invasion was seen: rupture of Bruch's membrane (87.7%), invasion of the retina (49.1%), tumor cells in the vitreous (25.2%), vortex vein invasion (8.9%), invasion of tumor vessels by tumor cells (13.8%), and invasion into emissary canals (55.0%). Overall, 81.1% demonstrated local invasion, excluding rupture of Bruch's membrane. Scleral invasion was present in 55.7% of eyes, and extrascleral extension was present in 8.2%. Mitotic activity was significantly reduced in eyes that had received preenucleation radiation treatment (P < .001). The number of macrophages in the tumor increased with increased pigmentation (P < .001) and increased necrosis (P < .01).

CONCLUSION

The accuracy of diagnosis in the COMS is high, with histopathologic confirmation of the diagnosis at 99.7%. Extensive local invasion of the tumor was seen. Preenucleation irradiation significantly reduced the number of mitotic figures. An association was found regarding the presence of macrophages, the level of pigmentation, and degree of necrosis.

Prognostic parameters in uveal melanoma: a review

Histologic cell type, largest tumor diameter and tumor location have traditionally been regarded as the leading predictors of survival for uveal melanoma. Morphological cell typing is, however, subjective to variations in interpretation. More objective classification parameters have emerged from extensive cytomorphometrical and DNA flow cytometrical studies. For patients with uveal melanoma there is no effective therapy if metastases have developed, and the median survival after clinical diagnosis of hepatic metastases is extremely poor. Current research focuses on the mechanisms underlying the metastatic process, including tumor vasculature, cytogenetics, oncogene activation, immunology, melanoma-associated antigens and tumor cell migration (cell-cell and cell-matrix interaction). Several new prognostic parameters have emerged from these studies, such as closed vascular patterns, loss of one chromosome 3, and different indices of cell proliferation. Furthermore, considerable genotypical and phenotypical differences have been found between uveal and cutaneous melanoma. In prospective studies on large series of melanomas a combination of histopathological and/or clinical prognostic parameters might be selected with high sensitivity and specificity, providing a way of selecting patients at high risk of developing metastatic disease, who might be eligible for adjuvant therapy.

Posterior uveal melanoma. The Swedish perspective

Posterior uveal melanoma is the most common primary intraocular malignant tumour and in Sweden some 70-80 new cases present each year. While uveal melanoma is more prevalent in the setting of ocular melanocytosis and neurofibromatosis, there is little conclusive data on the aetiology. Most patients experience a progressive visual field defect and present with a grey or greyish-brown mass of the posterior choroid. Diagnostic procedures include fluorescein angiography, ultrasound and magnetic resonance imaging. In some cases, intraocular biopsy may be required to make a correct diagnosis. Posterior uveal melanomas can usually be managed by any of a number of eye-preserving options like plaque radiotherapy and charged particle irradiation, but eyes containing large tumours are often enucleated. Nearly half of patients with posterior uveal melanoma, and in particular those with large tumours, ultimately succumb to metastatic disease. While most patients with tumour dissemination are treated with systemic chemotherapy possibly combined with interferon, metastatic spread confined to the liver may potentially be managed by intraarterial perfusion chemotherapy or liver resection. However, outcome of patients with systemic disease remains extremely poor with a median survival following detectable tumour dissemination of only two to five months. There are still insufficient data on the impact of various treatments on survival, but a large prospective trial addressing this issue is in progress. The present review summarizes the state-of-the-art knowledge and current management of posterior uveal melanoma from a Swedish perspective.

Correlations of Ki-67 and PCNA to DNA ploidy, S-phase fraction and survival in uveal melanoma

In 79 patients with uveal melanoma, the tumours were investigated by DNA flow cytometry and immunohistochemical staining of PCNA and Ki-67. S-phase as a continuous variable was significantly correlated with Ki-67 (P = 0.033), but not with PCNA. DNA ploidy was not correlated with either of the two antigens. Ki-67 was significantly correlated with histopathological type (P < 0.001) and tumour size (P < 0.001). Large tumours and epithelioid cell type were associated with a high frequency of Ki-67 positive cells. A high level of Ki-67 positivity (> or = 6.5%) was also associated with a shorter survival (P = 0.0037), and when adjusted for DNA ploidy, histopathological type and tumour size, Ki-67 in the multivariate analysis remained an important prognostic factor (P = 0.017).

Correlation of DNA ploidy and S-phase fraction with chemotherapeutic response and survival in a randomized study of disseminated malignant melanoma

DNA ploidy and S-phase fraction were measured by flow cytometry in the tumour tissue of 87 patients with disseminated malignant melanoma, who had been classified either as responders or with progressive disease in a study of the effects of 2 chemotherapeutic regimens. The patients had been randomized to receive treatment with dacarbazine (DTIC) and vindesine (Eldesine) with or without addition of cisplatin (Platinol). Tumour tissue was obtained from both the primary tumours and the last histologically verified metastases, but in some cases only the primary tumours or the last metastases could be evaluated. There was a significantly higher mean S-phase value in melanoma metastases from patients with complete or partial responses compared with patients with progressive disease. Neither the S-phase fraction of the primary tumour, nor the DNA ploidy of the primary tumour or of the last histologically verified metastases taken before inclusion into the study were associated with therapeutic response. In the multivariate analysis, both the anatomical location of the metastases and the S-phase fraction measured on the last metastases remained significant prognostic factors of response. In the univariate survival analysis, there was an association between high S-phase fractions of the metastases and longer survival. In the multivariate survival analysis, the S-phase fraction, the number of involved metastatic sites and the treatment response were independent predictive factors. We conclude that, in disseminated melanoma treated with chemotherapy, a high S-phase fraction measured in the last histologically verified metastases is associated with a higher response rate and a longer survival. Our results clearly support the role of S-phase measurement as a potential tool for selecting patients for treatment.