Prevalence of co-existent neoplasia in clinically diagnosed pterygia in a UK population

In our study from a single, UK-based tertiary pathology center, we received 2061 specimens submitted by ophthalmologists as possible pterygia over nearly 25 years. The rate of co-existent neoplasia in those specimens was only 0.6%, the vast majority of which were OSSN. This very low rate is consistent with some previous studies in geographic regions with lower levels of UVB exposure, despite our diverse population [5]. Studies which, like ours, included clinically suspicious lesions, found concomitant rates of OSSN in 0.3–9.8% of pterygium specimens, with higher rates in areas with higher UVB exposure [7,8,9].

In contrast, studies which excluded atypical lesions, found concomitant OSSN rates of 0–5% [5, 10]. Segev et al. found no OSSN in submitted pterygia samples, despite studying a population in a country of high UVB exposure, due in part to their exclusion of lesions which were considered suspicious clinically [6].

In our study, six cases had clinically atypical features, though only two cases were excised with full oncology precautions (wide margins, no touch technique and adjuvant cryotherapy). If we had excluded these pre-operatively suspicious lesions, the rate of incidental neoplasia would become only 0.3% in our study population. The proportion of the 2049 pterygium specimens without co-existent OSSN that had atypical features pre-operatively is unfortunately unknown.

In the three cases in the present study that had invasive neoplasia, one was found to be a melanoma. In pale skinned individuals with lightly pigmented irides, conjunctival melanoma can mimic OSSN [17]. It is important to bear this differential diagnosis in mind when the clinical features of a pterygium are atypical.

In two cases the “pterygium” turned out to be squamous cell carcinoma. The ethnicity of these were South Asian and African. Individual risk factors such as lifetime UV light exposure, immunosuppression or smoking history are not known in these cases. Both cases had clinically atypical features for a simple pterygium (nodule with inflammation or a gelatinous appearance). We would therefore advocate histopathological analysis for excised pterygia that display clinically unusual features.

Although histopathological analysis is the gold standard test, technological advances may assist in differentiating pterygia from OSSN. Use of in the clinic of vital dyes such as 0.05% Toluidine Blue vital staining for detecting cellular abnormality is of limited value, with high sensitivity but low specificity for OSSN [18]. More promising is anterior segment optical coherence tomography (AS-OCT) in detecting anatomical abnormality that is compatible with OSSN over pterygium [19] Rigorous testing of such devices may herald an era of a non-invasive tests to diagnose OSSN, followed by topical treatments—a notion that is being studied and may gain wider acceptance with results in various populations.

Although we had incomplete data on lesion location in three of the 12 cases, we found nasal location to be most common, consistent with previous reports [20]. Oellers et al. found inferior lesions to be more common in suspected OSSN [7].

Limitations of our study include the retrospective methodology. Moorfields Eye Hospital NHS Foundation Trust has multiple geographically distributed satellite sites within Greater London which send their histology specimens to the Department of Eye Pathology, each site with variable access to imaging, and varying levels of expertise in dealing with ocular surface malignancies. This has prevented us accessing long term follow up data for patients, and pre-operative information in some cases. Further prospective study is warranted to examine the rate of coexistent neoplasia with standardization of which lesions are considered typical or atypical.

Overall, we found the prevalence of co-existent neoplasia in pterygium specimens to be 0.6% in a UK-based population, but if we excluded clinically atypical lesions, this rate falls to 0.3%. This calls into question the time-honored doctrine of sending all excised pterygia for histopathological examination. This information will be useful in shaping clinicopathological pathways, of which specimens require histopathological diagnosis, particularly if imaging such as the AS-OCT leads us to “in vivo” biopsy. Rationing histology, however, would risk missing the rare occurrence of neoplasia in otherwise bland looking lesions, such as patient 2 in the present study, delaying diagnosis and potentially increasing the risk of locoregional spread.

It is the authors’ belief that in the UK population, experienced ophthalmologists can be reassured that the clinically typical pterygium is likely to be just that, especially if adjunctive investigations such as AS-OCT become more commonplace and prove reassuring. Histology remains crucial where there is clinical concern or recurrence of a previously excised lesion. This study may influence future guidance for the indications for submitting non-suspicious pterygia for histopathological examination.

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