DS18: Mohs micrographic surgery for the treatment of primary cutaneous mucinous carcinoma: a case series

Aine Kelly,¹ Rakesh Anand,² Jana Natkunarajah,³ Venura Samarasinghe¹ and Emma Craythorne²

¹St George's University Hospitals NHS Foundation Trust; ²Guy’s and St Thomas’ NHS Foundation Trust; and ³Kingston Hospital NHS Foundation Trust, London, UK

Primary cutaneous mucinous carcinoma (PCMC) is a rare adnexal tumour of the skin. It is a slow-growing tumour that rarely metastasizes but carries high morbidity owing to its high rate of recurrence. It typically occurs in the periorbital region followed by other areas of the head and neck. Wide local excision with 1–2 cm margins has been the standard treatment, but, in recent years, treatment with Mohs micrographic surgery (MMS) has been reported. We identified PCMC treated with surgery across two tertiary MMS referral centres. Cases were identified via a surgical database and retrospective histopathology reports from 2015 to 2021. All patients had imaging to exclude mucinous carcinoma from another organ metastatic to the skin. A total of 10 patients with a histopathological diagnosis of PCMC were identified. Nine patients were treated with MMS and one was treated with conventional wide local excision. Nine patients had periorbital lesions and one had a PCMC on the scalp. The preoperative size of the primary cutaneous lesion varied from 2 × 2 mm to 17 × 13 mm, with the average preoperative area being 80·2 mm. Postoperative defect size varied from 6 × 6 mm to 32 × 9 mm and was anatomically location dependent. Follow-up of lesions was for 2 years, although many patients were also discharged to their referring hospital for ongoing follow-up after this time. There was no recurrence of PCMC treated with MMS during the follow-up period. One of the 10 patients treated with MMS had recurrent PCMC from previous conventional surgery. The one patient treated with conventional surgical excision had three recurrences over a 5-year period. Each surgery was completed, with wide local margins of 1–2 cm requiring grafting and flap reconstruction. Their final procedure was completed via slow frozen section. Despite this, they have had positive margins and have been referred for radiation treatment. The periorbital location of PCMC, the easily discernible histopathology and the high recurrence rate makes these tumours ideal for treatment with MMS. The high recurrence rate for PCMC vs. other skin tumours treated with MMS may be related to the ability of this tumour to have skip lesions leading to falsely clear margins, the cystic nature of this tumour leading to iatrogenic seeding upon incision or technical error due to lack of familiarity with tumour histopathology. We postulate that a slightly wider margin should be taken for PCMC than the traditional 1–2 mm margin used for basal cell carcinomas treated with MMS. This is the largest series of PCMC treated with MMS, with only four previous series described. We demonstrate that MMS is a more effective treatment for primary mucinous carcinoma of the head and neck and should be the treatment of choice where available.