Epidemiology of squamous cell conjunctival cancer.

The etiology of squamous cell carcinoma of the conjunctiva (SCCC) is not well known. A possible role of UVB radiation is suggested by an excess of SCCC in tropical countries and by the association between squamous cell skin cancer and exposure to UVB. Human papillomavirus type 16 also may be involved, given that it has been detected in benign and malignant conjunctival lesions and is the primary etiological agent involved in carcinoma of the anogenital tract. To examine the relationship between UVB exposure and SCCC, population-based age-adjusted incidence rates of SCCC and of conjunctival melanoma and squamous cell cancer of the eyelid were plotted against the UVB insolation of each registry site. Incidence data were examined further for patterns of second primary cancers among people with SCCC. SCCC was rare in the United States, with an incidence rate of 0.03 per 100,000 persons, although the rate was approximately 5-fold higher among males and whites. Regression analysis suggested a link between UVB exposure and SCCC rates (beta = 2.25; r = 0.58) that was as strong as that for squamous cell carcinoma of the eyelid (beta = 2.73; r = 0.62) and much stronger than for conjunctival melanoma (beta = 0.28; r = 0.02). Risk of a second malignancy after SCCC was not increased overall (20 observed and 14.1 expected), although a significant excess of salivary gland cancer (4 observed and 0.03 expected) and a borderline excess of lung cancer (6 observed and 2.4 expected) were noted. These observations suggest that UV radiation likely contributes to SCCC development. Additional research is needed to define the other exposures and host susceptibility that likely interact with UV-related genetic damage in the multifactorial development of this rare neoplasm.