The first part of this thesis summarizes the current literature on small choroidal melanomas (CMs). Although the aetiology of this disease remains unknown, many risk factors have been reported. Differentiation from the more common choroidal naevi is generally clinical, and several typical characteristics of the malignant tumour have been used as a diagnostical tool. When the differentiation cannot be made clinically or by biopsy, the remaining option is to observe for growth that signals malignancy. Small posterior tumours, in particular, have frequently been observed for growth because treatment would most likely affect vision. However, observation before treatment might increase the risk for metastases. Small CMs are typically treated conservatively, and enucleation is no longer a generally accepted alternative, partly because these tumours are thought to be able to micrometastasise years before diagnosis. The primary aims when managing small malignant CMs are to destroy the tumour and prevent local recurrences that might be associated with an increased risk for metastases. Eye-preserving treatments frequently allow for the preservation of useful vision as well. Several options are available for treating small CMs. In Finland, the majority of CMs are treated with episcleral plaque brachytherapy. Ruthenium106 brachytherapy is an effective choice for small melanomas because the dose distribution is ideal for treating tumours with a thickness of up to 5.4 mm. The second and main part of this thesis summarizes the recent Finnish contributions to this field. The research presented in this thesis starts by retrospectively examining the treatment results from 10-mm ruthenium plaque (Study I), leading to a comparative study looking at the treatment results of both 10-mm round radioactive plaque (CCX) and 15-mm round radioactive plaque (CCA), with the aim to see whether and when it is safe to reduce vision- threatening radiation side-effects by using a smaller plaque (Study II) when treating small CMs less than 10 mm in their largest basal diameters (LBDs). The smallest 10-mm plaque delivers less scattered radiation compared with a 15-mm plaque or larger. Previously, it was not known whether a smaller radiation area and less scattered radiation could affect the recurrence rate, preservation of useful vision, and frequency of side-effects. This thesis found that the recurrence and complication rates were comparable between patients treated with the 10-mm or 15-mm plaque, but vision was more effectively preserved after treatment with the 10-mm plaque when the tumour was located close to the foveola. An eccentric location of the plaque was a risk factor for a local recurrence with both plaques. This study supports the treatment of small posterior CMs close to fovea with 10-mm rather than 15-mm plaque. The challenge of diagnosing small CMs before they have the capacity to disseminate led to the search for the smallest size of a CM that had been reported to metastasize and an attempt to find out whether melanomas that disseminated and melanomas that did not disseminate differed from each other clinically. As the Finnish population is not sufficiently large to collect data for this study, a retrospective collaboration study was done with the European Ocular Oncology Group (OOG) (Study III). Ten ocular oncology services submitted the data on all their patients with a CM of 3 mm or less in thickness and 9 mm or less in LBD who were treated and who subsequently developed metastases. This study found that CMs less than 3 mm in LBD are unlikely to metastasize. Observation without treatment beyond this limit might impair survival. Clinical characteristics of small fatal choroidal melanomas (SFCMs) did not differ from those of non-fatal CMs of a similar size: clinical characteristics predicting metastasis could not be identified. Due to inspiration from Study III, ways to alternatively diagnose small melanomas before they get the capacity to disseminate were examined. The growth rates and tumour doubling times (TDT) of incipient CMs were calculated (Study IV). Short TDT and a fast growth rate combined with the calculated age at tumour origin after puberty supported a melanoma diagnosis. These were the nine smallest presumed CMs reported at that point. The earlier diagnosis enabled treating these patients with less invasive transpupillary thermotherapy (TTT), of which preliminary results are shared in this thesis. The reported growth parameters could be employed as diagnostic criteria for the incipient melanomas.
|Place of Publication||Helsinki|
|Publication status||Published - 2020|
|MoE publication type||G5 Doctoral dissertation (article)|
Bibliographical noteM1 - 78 s. + liitteet
Fields of Science
- 3125 Otorhinolaryngology, ophthalmology