Epidemiology of ocular surface squamous neoplasia in Africa

Abstract

Objectives: To describe the epidemiology and an aetiological model of ocular surface squamous neoplasia (OSSN) in Africa.

Methods: Systematic and non-systematic review methods were used. Incidence was obtained from the International Agency for Research on Cancer. We searched PubMed, EMBASE, Web of Science and the reference lists of articles retrieved. Meta-analyses were conducted using a fixed-effects model for HIV and cigarette smoking and random effects for human papilloma virus (HPV).

Results: The incidence of OSSN is highest in the Southern Hemisphere (16° South), with the highest age-standardised rate (ASR) reported from Zimbabwe (3.4 and 3.0 cases/year/100 000 population for males and females, respectively). The mean ASR worldwide is 0.18 and 0.08 cases/year/100 000 among males and females, respectively. The risk increases with exposure to direct daylight (2-4 h, OR = 1.7, 95% CI: 1.2-2.4 and ≥5 h OR = 1.8, 95% CI: 1.1-3.1) and outdoor occupations (OR = 1.7, 95% CI: 1.1-2.6). Meta-analysis also shows a strong association with HIV (6 studies: OR = 6.17, 95% CI: 4.83-7.89) and HPV (7 studies: OR = 2.64, 95% CI: 1.27-5.49) but not cigarette smoking (2 studies: OR = 1.40, 95% CI: 0.94-2.09). The effect of atopy, xeroderma pigmentosa and vitamin A deficiency is unclear.

Conclusions: Africa has the highest incidence of OSSN in the world, where males and females are equally affected, unlike other continents where male disease predominates. African women probably have increased risk due to their higher prevalence of HIV and HPV infections. As the survival of HIV-infected people increases, and given no evidence that anti-retroviral therapy (ART) reduces the risk of OSSN, the incidence of OSSN may increase in coming years.

Keywords: conjunctival intraepithelial dysplasia; conjunctival intraepithelial neoplasia; conjunctival squamous cell carcinoma; incidence; ocular surface epithelial dysplasia; ocular surface squamous neoplasia; risk factors.

Figure 1

A range of clinical presentations of ocular surface squamous neoplasia (OSSN) in East Africa. (a) Small lesion with leukoplakia; (b) Medium sized lesion with pigmentation; (c) Large lesion with corneal extension but not involving the fornices; (d) Very large lesion extending into the orbit.

Figure 2

Worldwide mapping of the age-standardized incidence rates (ASR) of squamous cell carcinoma of the eye (ICD-O-3 C.69) for the period 1998–2002 (Curado et al. 2007). Key: Dot size is directly proportional to incidence. Males are shown in blue and females in red. Overlaps between males and females appear purple in colour.

Figure 3

The age-standardized incidence rates (ASR) of squamous cell carcinoma of the eye (ICD-O-3 C.69) for the period 1998–2002 (Curado et al. 2007).

Figure 4

Sudden rise in the annual incidence rates of conjunctival SCCC in Kampala with the onset of the HIV pandemic – number of cases shown (Ateenyi-Agaba 1995).

Figure 5

Meta-analysis of case-control studies of HIV infection in ocular surface squamous neoplasia (OSSN) in Africa (fixed effect).

Figure 6

Meta-analysis of case-control studies of human papilloma virus (HPV) infection in ocular surface squamous neoplasia (OSSN) (random effects).

Figure 7

Meta-analysis of case-control studies in Uganda on cigarette smoking and ocular surface squamous neoplasia (OSSN) in Africa (fixed effect).

Figure 8

An aetiological model illustrating how ocular surface squamous neoplasia (OSSN) might develop. MMPs, matrix metalloproteinases; TIMPs, tissue inhibitors of metalloproteinases.