Sebaceous Neoplasms With Rippled, Labyrinthine/Sinusoidal, Petaloid, and Carcinoid-Like Patterns: A Study of 57 Cases Validating Their Occurrence as a Morphological Spectrum and Showing No Significant Association With Muir–Torre Syndrome or DNA Mismatch Repair Protein Deficiency

Abstract: Sebaceous neoplasms with an organoid pattern (rippled, labyrinthine/sinusoidal, carcinoid-like, and petaloid) are rare. Previous studies suggested that the above patterns likely represent variations along a morphological continuum. The objectives of this study were to (1) validate this proposition by studying a large number of cases, (2) determine whether there are specific associations with clinical features, (3) establish their frequency, and (4) determine whether they have any association with Muir–Torre syndrome. Fifty-seven sebaceous neoplasms (54 sebaceomas and 3 sebaceous carcinomas) with organoid growth patterns were studied. These occurred in 36 men and 18 women (sex unknown in 3), with ages at diagnosis ranging from 22 to 89 years (mean, 63 years). All patients presented with a solitary nodule (mean size, 11 mm) on the head and neck area. Of the 57 tumors, 24 manifested a single growth pattern, 23 had a combination of 2 patterns, and 10 a combination of 3 patterns, indicating that these patterns are part of a morphological continuum of changes. The carcinoid-like pattern was the most frequent in the "monopatterned" neoplasms (13 cases), whereas the labyrinthine/sinusoidal pattern comprised most of the "polypatterned" lesions, in which various combinations occurred. Immunohistochemically, mismatch repair protein deficiency was detected in 3 of the 22 cases studied, whereas 5 of the 33 patients with available follow-up had an internal malignancy/premalignancy. In conclusion, sebaceous neoplasms with organoid growth patterns are predominantly sebaceomas having a predilection for the scalp, occurring as solitary lesions in elderly patients (male to female ratio of 2:1). Such patterns are expected to be found in a quarter of sebaceomas. In most cases, more than one of the organoid patterns is present. These lesions do not appear to be associated with internal malignancy or mismatch repair deficiency in most cases. However, confirmation of the absence of any significant association with Muir–Torre syndrome syndrome will require genetic studies.

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