Cutaneous tumoural melanosis: a presentation of complete regression of cutaneous melanoma

The Prognostic Significance of Tumoral Melanosis

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.

Spontaneous resolution of lentigo maligna: a case report

A 64-year-old man with a known history of psoriasis was under regular clinical and reflectance confocal microscopy follow-up for a biopsy-proven lentigo maligna on his right forehead. Five years after the initial diagnosis the lesion gradually disappeared with no concurrent effective treatment. Spontaneous resolution is reported in various skin tumours but to our knowledge, this phenomenon has not been previously described in lentigo maligna.

Regression in cutaneous melanoma: histological assessment, immune mechanisms and clinical implications

Tumour regression is an immunologically driven process that results in complete or partial disappearance of tumour cells. This can be observed in histological sections as replacement of tumour cells with fibrosis, angiogenesis, and a variable inflammatory infiltrate. In primary cutaneous melanoma, the prognostic significance of regression has been debated for decades, in part because inconsistent histological criteria are used in prognostication studies. It is broadly accepted that CD8+ T lymphocytes are the primary effectors of the anti-tumour response, but the interplay between melanoma and the immune system is complex, dynamic, and incompletely understood. Sustained progress in unravelling the pathogenesis of melanoma regression has led to the identification of therapeutic targets, culminating in the development of immune checkpoint inhibitors for the management of advanced disease. Modern techniques allow for high-resolution spatial analyses of the tumour microenvironment. Such studies may lead to better understanding of the immune drivers of melanoma regression, thereby facilitating the search for new prognostic and predictive biomarkers to assist clinical decision-making.

Papulonodular pigmented lesions in a patient with Stage IV malignant melanoma

A 78-year-old man received immunotherapy for in-transit metastatic melanoma papulonodules on his left lower abdomen in the form of intralesional injections of talimogene laherparepvec (T-VEC), an oncolytic genetically modified herpes virus. Despite therapy, the colour and size of the lesions remained clinically unchanged; however, histopathological examination revealed only melanophages in the absence of melanoma cells. The diagnosis of tumoral melanosis secondary to immunotherapy with T-VEC was made. This case emphasizes the importance of histopathological evaluation in assessing response to immunotherapy of in-transit metastatic melanoma lesions.

Peritoneal melanosis associated with metastatic melanoma previously treated with targeted and immune checkpoint inhibitor therapy

Peritoneal melanosis is an uncommon benign condition, the pathophysiology of which is unclear. Macroscopically, it appears as diffuse dark brown or black pigmentation within the peritoneum, mimicking more sinister conditions such as metastatic melanoma. It has been described in a variety of contexts, but only exceedingly rarely in association with metastatic melanoma, with only two previous published case reports. We present a case of peritoneal melanosis associated with metastatic melanoma involving the spleen, previously treated with targeted and immune checkpoint inhibitor therapy. With increasing reports of melanoma regression manifesting as cutaneous tumorous melanosis in patients treated with immune checkpoint inhibitors, we postulate that, similarly, immunotherapy and tumour regression might have a role to play in the pathogenesis of the peritoneal pigmentation in this case.

Reporting regression in primary cutaneous melanoma. Part 1: history, histological criteria and pathogenesis

Regression is an important histopathological parameter reported for the diagnosis of primary cutaneous melanoma. Histological regression is defined by The College of American Pathologists as the replacement of tumour cells by lymphocytic inflammation, with attenuation of the epidermis, and nonlaminated dermal fibrosis with inflammatory cells, melanophagocytosis and telangiectasia. Histological regression may be reported as absent versus present and, if present, as complete, partial or segmental. The stages of histological regression are early, intermediate and late, depending on the extent of histological inflammation and fibrosis. Regression occurs when the host's immune system attacks primary melanocytic tumour cells via tumour-infiltrating lymphocytes, resulting in fibrosis. The immunological mechanisms driving complete, partial and segmental regression may vary. In this first part of this two-part review, we review the history, histological criteria and pathogenesis of regression in primary cutaneous melanoma, while in Part 2 we will review the effect of histological regression on prognosis, evaluation and management.

Metastatic Melanoma Negative for 5 Melanocytic Markers, Complete Regressed Primary Cutaneous Melanoma, and Melanoma-Associated Leukoderma in the Same Patient

Melanomas with complete histological regression have been seen very infrequently. On the other hand, the diagnosis of metastatic melanoma is based on the histopathology and positivity of markers such as S100, Melan-A, and HMB-45 whose sensitivity is 99%, 82%, and 76%, respectively. It is very rare that metastatic melanomas and even more primary melanoma are negative for all of these markers. In these rare cases, there is usually a known primary. We present the case of a 82-year-old woman with a erythematous mass in the left groin and a 1-cm black-bluish irregular nodule on the skin of the ipsilateral foot. This lesion was clinical and dermoscopically compatible with primary melanoma. In the histological evaluation of the skin, a dermis full of melanophages and hemosiderophages were found in a background of fibrosis, scarce lymphocytic infiltrate, and neovascularization. Any cells expressing melanocytic markers were observed. It was diagnosed as tumoral melanosis. Lymph nodes showed a proliferation of atypical epithelioid cells with eosinophilic cytoplasm. Mitosis was conspicuous. Tumoral cells were vimentin and CD99 positive, and S100, CD34, HMB-45, Melan-A, SOX 10, tyrosinase, C-KIT, CD45, and CKAE1/AE3 negative, and BRAF-V600 mutated was detected. During follow-up, atypical vitiligo-like lesions were discovered, suggesting the diagnosis of metastatic melanoma totally regressed in our patient.