The Prognostic Significance of Tumoral Melanosis

Abstract

Background: Tumoral melanosis (TM) is a histological term to describe a nodular aggregation of macrophages containing melanin pigment (melanophages) that is devoid of viable melanocytes. It is most often identified in skin, where it may be appreciated clinically as a pigmented lesion; however, it can also be found in other organs such as lymph nodes. The presence of TM is usually thought to signify the presence of a regressed melanoma or other pigmented tumor. Until recently, it was a relatively uncommon finding; however, with the use of effective systemic therapies against melanoma, its occurrence in histological specimens is more frequent.

Methods: We identified and reviewed all histopathological diagnoses of TM at any organ site reported at a single institution from 2006 to 2018. TM cases were paired with non-TM cases of cutaneous melanoma through propensity score matching at a 1:2 ratio, and their survival outcomes were compared. The clinical outcomes examined included recurrence-free survival (RFS), distant disease-free survival (DDFS), melanoma-specific survival (MSS), and overall survival (OS).

Results: TM was reported in 79 patients. Their median age was 65 years (range 22-88), with a 2:1 male predominance (51 out of 79, 65%). The most common organ involved was the skin (67%), with a third of all cases localized to a lower limb (36%). TM had a strong association with the presence of melanoma (91%) and regression at other sites of melanoma (54%), suggesting that it is part of a systemic immune response against melanoma. Most patients with TM either previously or subsequently developed histologically confirmed melanoma in the same anatomical region as the TM (89%). Thirty-five TM patients were matched with 70 non-TM cases. Patients with melanoma who developed TM without prior regional or systemic therapy showed improved MSS (p = 0.03), whereas no statistically significant differences were observed in terms of RFS, DDFS, and OS.

Conclusions: TM usually occurs in the context of a previous or subsequent cutaneous melanoma and is associated with improved MSS. It is important that TM is recognized by pathologists and documented in pathology reports.

Keywords: immunotherapy; melanoma; melanophages; melanosis; pathology; pigmentation; prognosis; regression; treatment; tumoral.