Keratoacanthomas following definitive volumetric modulated arc radiotherapy for skin field cancerization
We describe three cases of keratoacanthomas (KAs) following definitive volumetric modulated arc therapy (VMAT) for skin field cancerisation (SFC). One lesion arose on a back in an area that had received a total of 30.6 Gy in 17 fractions. It first became apparent at 24 days post RT and resolved without treatment by 150 days. The other arose on a nasal alar in the beam penumbra that received 36Gy in 25 fractions, appearing at 57 days and resolving without treatment by 85 days. A third case occurred in an immunosuppressed patient. She developed KAs in one of two areas irradiated with lesions appearing at 21 days post RT and finally resolving at 300 days despite acitretin. The area received a total dose of 41.4 Gy in 23 fractions. Spontaneous resolution of index KA confirmed the diagnosis in all cases. On average, the patients were 79 years of age, the area bearing the KA had received an average of 36Gy in 22 fractions. The average onset of the KAs was 24 days or 3.5 weeks or one month after RT, and always soon after reepithelization was completed. Resolution was at an average of 168 days or 24 weeks or 6 months after the completion of RT. In all three cases other lesions arose adjacent to them and, in each case, one of these other lesions was excised with histopathology confirming squamo-proliferative lesions. There has been no recurrence at least 6 months after the last follow up. To our knowledge these are the first three cases of KA described following definitive VMAT for SFC. The possibility of KA arising after RT does need to be considered during the consent process.