Limbal Stem Cell Preservation During Proton Beam Irradiation for Diffuse Iris Melanoma

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To the Editor:
We read with great interest the article titled “Limbal Stem Cell Preservation During Proton Beam Irradiation for Diffuse Iris Melanoma” by Singh et al.1 In this article, prophylactic stem cell autografting involved removing the patient's own limbal stem cells before proton irradiation to preserve their function. This tissue was preserved (outside of the patient) during proton irradiation of the entire anterior segment for iris melanoma. Then, after irradiation of the anterior segment (including the surgical wound—graft bed), the patient's stem cell tissue was regrafted into its original anatomic surgical site. These extra 2 procedures were performed to preserve the patient's corneal epithelial function.
However, in this article, Dr. Singh quotes Shields, Rundle, and Konstantinidis to support the need for stem cell autografting surgery.2–4 In review of these articles, the article by Shields in 2013 was not on total anterior segment iodine-125 plaque irradiation but noted 22/144 (15%) cases with secondary corneal disease.2 These included corneal edema, corneal abrasion, corneal ulcer, and stem cell deficiency, but no subgroup analysis was provided. In Rundle's series of 15 patients treated with proton beam, 11 were diffuse iris melanomas, and we could find no mention of corneal opacity or stem cell deficiency.3 Last, Konstantinidis reported on 12 diffuse iris melanomas treated with proton beam.4 They decided that they would use contralateral stem cells if “uncontrollable” stem cell deficiency arose; however, they had no such cases. Finally, in our own literature review, we found Willerding's recent series of 54 cases of proton beam irradiation for diffuse iris melanoma.5 In that relatively large series, there were 2 cases of poorly healing corneal abrasions and only 1 resulting in opacity.
Clearly, the literature suggests that iris melanomas (diffuse and partial) are being treated with eye and vision-sparing radiation therapy (iodine-125, palladium-103, and proton beam).2,5–8 However, we see no medical evidence to support preirradiation stem cell autografting.

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