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Pterygium as Predictor of Cutaneous Melanoma

A cohort study conducted in Australia found that pterygium can be used as a predictor of cutaneous melanoma. Several studies have tried to find the relationship between the mechanism of pathogenesis in these two diseases. But so far, no explanation has been found for the relationship between pterygium and cutaneous melanoma. These two diseases are linked with the same etiology, so they are often found to co-occur.

Pterygium
Source:https://drbrendancronin.com.au/pterygium


Pterygium

Pterygium is a lesion on the eyeball surface, which is characterized by elastotic degeneration and fibrovascular proliferation in the conjunctival limbus.

Clinical manifestations of pterygium are extraocular, superficial, prominent masses that usually form from the perilimbal conjunctiva to the corneal surface. Pterygium can manifest from mild conditions in the form of atrophic lesions to severe forms of aggressive and rapidly growing fibrovascular lesions. Pterygium can interfere with vision by causing red eyes, astigmatism, and visual axis obstruction.

Pterygium was found to be associated with exposure to ultraviolet radiation. Other risk factors are living in the tropics and subtropics and work that requires outdoor activities related to the intensity of exposure to ultraviolet radiation.

Cutaneous Melanoma

Melanoma occurs through melanomagenesis involving many progressive genetic mutation processes. Genetic mutations can induce cell proliferation, differentiation, and death and cause susceptibility to the effects of carcinogenesis by ultraviolet radiation.

Some risk factors for melanoma are skin sensitivity to sunlight, sun exposure in children, blazing sun, increased number of nevus, family history of melanoma, and age. Some other associated risk factors are gender, history of melanoma, and large congenital nevus (> 20 cm diameter) in adulthood.

Studies regarding pterygium related Incidence of Cutaneous Melanoma

A cohort study conducted in Australia involved 23,625 the pterygium cases from 1979 to 2014. The controls in this study were subjects without pterygium, gender, age, and subject residence, which were commensurate with the case group. 1957 cases of cutaneous melanoma were found in both groups, and statistically significant differences were found between groups.

This study reported that there was an increase in the likelihood of 24% for pterygium sufferers who have undergone treatment for cutaneous melanoma after statistical control over age, gender, location of residence, and type of pterygium management performed on the patient. Also, a relationship was found between the age of the patient when he received pterygium management and the diagnosis of cutaneous melanoma. After controlling for other predictor factors, there is an increased risk of 2% for each year of increasing age, while being treated.

A national cohort study conducted previously in Taiwan found that of 19,701 patients with pterygium, there were 7 patients with malignant melanoma. The incidence in the pterygium group was almost 2 times higher than in the control group, but the hazard ratio in the two groups was not significantly different.

Research has tried to find an association of pathogenesis mechanisms in these two diseases. One of them is a study conducted in Italy in 2002. This study aims to analyze the relationship of excessive exposure to sunlight and ultraviolet radiation as the most prominent environmental predisposing factor in pterygium and melanoma.

Genetic studies have found that there are similarities in genetic mutations in pterygium and melanoma. In both diseases, there is a decrease in the chromosome heterozygosity of the 9p21 region.

The study also aims to determine the presence of antigens associated with melanoma in pterygium tissue to determine the pathophysiological relationship between the two.

In this histopathological study, pterygium tissue only showed immunoreactivity on one melanoma-specific antigen, i.e., S100 staining. Another immunohistochemical staining that is melanoma-specific, HMB45 and Melan A staining, does not show immunoreactivity in pterygium tissue. In this study, no correlation was found between pterygium and melanoma.

To date, there is no pathophysiologic explanation for the association between pterygium and cutaneous melanoma. Both of these diseases are only associated with the same etiology, namely in ultraviolet radiation, so they are often found to co-occur.

Pterygium is mostly found in climates that get long exposure to sunlight. The pathophysiology between pterygium and ultraviolet radiation is not well known but is associated with extracellular cellular remodeling through the stimulation of the work of cytokines and other immunological agents.

The relationship between ultraviolet radiation with cutaneous melanoma has been widely studied. Skin conditions such as skin color, burns, and sunfish are associated with the occurrence of cutaneous melanoma. The study found that total sun exposure is closely related to cutaneous melanoma. However, it has been found that intermittent exposure to ultraviolet radiation has a higher risk association than populations exposed to continuous ultraviolet light.

Intermittent exposure occurs, for example, when on vacation to areas with much sun exposure such as beaches. Ultraviolet radiation causes cutaneous melanoma through DNA mutations. Exposure to ultraviolet light can cause the formation of pyrimidine dimers or cytosine and thymidine deamination. The vulnerability of this DNA mutation is also influenced by familial mechanisms that are not yet known. Allegedly increased sensitivity to ultraviolet light is associated with an increased risk of melanoma.



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