Human papillomaviruses and their association with squamous cell carcinoma of the conjunctiva

Abstract

Squamous cell carcinoma of the conjunctiva (SCCC), hitherto a rare cancer, has increased manyfold since the advent of HIV/AIDS. Solar ultra violet radiation (UV) may also be a risk factor for the disease. The increased incidence has led to the hypothesis of an infective agent as a risk factor, especially infections with human papillomaviruses (HPV) types 16 and 18. The main purpose of this thesis was to study the association between these factors and SCCC.

Pilot studies I and II. Aims: to assess the feasibility and test methods for a larger case control study in Uganda; to investigate the presence of HPV in conjunctival tissue using broad spectrum PCR; to investigate the presence of UV induced mutations in the TP53 gene in SCCC samples. Methods: 21 SCCC cases and 22 control patients were tested for the presence of HPV in conjunctival tissue; the DNA from the samples was further analyzed for the presence of somatic mutations in the T53 gene. Results: Cutaneous HPV were found in 86% cases and 36% controls, suggesting a role of cutaneous HPV in the aetiology of SCCC. Seven of the mutations were CC to TT transitions, which are characteristic of solar UV light DNA damage.

Study III. Aims: to assess the presence of HPV in lesion-free conjunctiva and assess whether there is an excess of HPV infection in concurrent HIV/AIDS disease. Methods: 136 lesion-free frozen conjunctival samples from autopsies performed at Mulago hospital, Kampala, Uganda, were analyzed for the presence of HPV using broad spectrum PCR methods. Results: 14.6% samples tested positive for cutaneous HPV, and no mucosal HPV infection was detected; no excess of HPV infection was found in individuals who had died of HIV/AIDS-related causes as compared to those who had died of other diseases. Conclusion: HPV infection occurs in the conjunctiva: there was no excess of HPV infection in HIV/AIDS patients as compared to other patients, though we cannot rule out the possibility of the misclassification of HIV/AIDS patients.

Study IV. Aims: to compare the prevalence of HPV infection in SCCC patients patients with other eye diseases. Methods: Hospital-based case control study in Mulago and Jinja Hospitals, Uganda, involving 94 cases of SCCC and 285 controls with other eye diseases. We compared the prevalence of HPV infection in 94 biopsies of SCCC patients to 285 biopsies from hospital control patients with other eye diseases. Highly sensitive broad spectrum PCR tests that detect up to 75 types of HPV were used to analyze the frozen tissue biopsies. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were computed, adjusting for age, sex and HIV status. Results: cutaneous HPV were detected in 44.7% of the SCCC cases and 10.5% in controls (OR = 6.22; 95% CI = 3.60-10.72). The strength of the association of cutaneous HPV with SCCC was stronger in multiple infections than single infections, (OR = 74.2; 95% CI = 23.4-235.7) and (OR = 12.8; 95% C = 5.5-29.6) respectively. Mucosal types were detected in 6.4% SCCC and 3.5% controls (OR = 1.0; 95% CI = 0.-2.9). HPV5, 8 and 24 were most common in SCCC. The association of cutaneous HPV with SCCC was stronger in SCCC patients with HIV (OR = 17.0; 95% CI = 5.5-52.5). HIV infection was detected in 85.1% SCCC and 44.9% controls, (OR = 7.3; 95% CI = 4.2-12.4). There was no significant association of SCCC with age, sex, educational level, smoking habits, indoor or outdoor occupation. Conclusion: Cutaneous HPV and HIV are significantly associated with SCCC, while mucosal HPV are not significantly associated.