Non-choroidal yellow melanoma showing positive staining with Sudan Black consistent with the presence of lipofuscin: a case report

A case of a predominantly yellow primary superficial spreading melanoma arising on the back of a 44-year-old woman is presented. Possible causes of the clinical and dermatoscopic yellow color are discussed. Staining with the histochemical stain, Sudan Black, revealed a differential uptake compared to a closely matched control melanoma. We speculate that the clinical and dermatoscopic yellow color could be due to the presence of increased amounts of the pigment lipofuscin, which is known to produce subtle orange color in some choroidal melanomas.

Following this, in an attempt to clarify the cause of yellow color, two further stains were performed.
A pearl's stain confirmed the absence of hemosiderin.
To test for the presence of the pigment lipofuscin, new sections were cut from the paraffin block, five microns in thickness and stained with Sudan Black. When this appeared to stain heavily, new sections of the same thickness were also cut from the paraffin block of another melanoma as a control and stained with Sudan Black. The control melanoma was a heavily pigmented superficial spreading melanoma, also with a dominant (pigmented) nodule, with a Breslow thickness of 2.2 mm, 2 mitoses per mm 2 , and no ulceration.    47 [1], amelanotic/hypomelanotic melanomas (AHM) typically present with minimal clues due to melanin structures on which to base a diagnostic analysis [2]. The particular challenge, where a melanoma presents clinically as a hypomelanotic nodule, has been described as that of evaluating a rapidly enlarging pink tumor [3]. The melanoma reported here was a hypopigmented superficial spreading melanoma ferential staining with Sudan Black in the upper image (case subject to this report) compared to the control.

Conclusions
While pigmented melanomas usually display dermatoscopic disorganization and clues related to their chaotic evolution    Observation | Dermatol Pract Concept 2013;4(2):9 [15]. Sebum consists primarily of a complex mixture of lipids [17]. Ideally staining for lipids is performed on fresh unfixed tissue with stains such as Oil Red O. In this case all tissue had been fixed in formalin and blocked in paraffin.
Subtle orange pigment, attributed to the pigment lipofuscin, a derived lipid which is an accumulation of lysosomes [18], is described as one of the features that can help differentiate choroidal melanoma from choroidal nevus [19]. The histochemical stain Sudan Black can be used on formalinfixed, paraffin-processed tissue to detect some phospholids and also lipofuscin [18]. The melanoma reported here showed significant staining with Sudan Black compared to staining by a similar but deeply pigmented melanoma. This increased staining was present in varying intensity and uneven distribution throughout the dermal component of the melanoma consistent with the uneven presence of dermatoscopic structureless yellow (Figure 2).
The possible presence of the pigment lipofuscin in this melanoma is supported by positive staining by Sudan Black, and we speculate that the structureless yellow color displayed clinically and dermatoscopically may be due to the pigment lipofuscin, a pigment which has been previously described as a clue to choroidal melanoma.
(SSM) with a dominant nodule, which was notable because of its dominant structureless yellow color. In one series of four cases of AHM with dermatoscopic images, all cases had significant pink or red color and none had any yellow color [4]. Although this lesion fulfilled the definition of AHM, according to revised pattern analysis (RPA), the presence of any pigment should lead to a diagnostic analysis based on pigmented structures [5,6]. Applying the RPA algorithmic method for pigmented lesions, "Chaos and Clues" [1] this lesion was asymmetric by color and therefore was regarded as exhibiting chaos (defined as asymmetry of structure and/ or color), and it had the clue of blue or gray structures so excision biopsy was indicated. In addition to these pigment clues, there were vascular dermatoscopic clues including an eccentric structurless pink area (Figure 2 upper pole) and a random arrangement of polymorphous vessels. Both milky red pink areas and linear irregular vessels are described as clues to AHM by Menzies et al. [7], and an eccentric structureless area (any color except skin color, including pink) and polymorphous vessels have been evaluated as clues to malignancy in RPA [8].
Dermatoscopic yellow color has also been attributed to keratin as seen in seborrheic keratosis [9] and congenital type nevus [10]. In a study of 400 BCCs Bellucci et al. found that 10% displayed yellow structures either as milia-like cysts (7.75%) or lobular structures (4.2%) [11], also presumably due to keratin. There was no accumulation of keratin to explain the yellow color in the melanoma reported here.
Structureless dermatoscopic yellow color has also been attributed to ulceration with surface serum exudate [6], and dermatoscopic structureless yellow color was described in the first case report of a balloon cell melanoma (BCM) with dermatoscopy [12], being attributed by the authors to ulceration.
Considering the possibility that it may actually have been the balloon cells that caused the yellow color, the only other reported BSM with dermatoscopic images was a partially pigmented lesion with a dominant structureless white area and without any yellow color [13]. The case we report here did have two cell populations, including one with large cells with vacuolated cytoplasm resembling balloon cells (Figures 6 A, C, D), but it did not meet the criteria for diagnosis as a BCM which requires that the melanoma contain more than 50% of balloon cells, [14] and in fact the sheets of balloon cells were only present focally. With respect to ulceration as a reported cause of structureless yellow in one melanoma [12], there was no evidence of ulceration either clinically, dermatoscopically or dermatopathologically in the case reported here.
Another published cause of dermatoscopic yellow is the presence of sebaceous structures in sebaceous hyperplasia [15], nevus sebaceous and sebaceous adenoma [16]. Bryden et al. attributed the yellow color in sebaceous hyperplasia to sebum accumulation by proliferation of sebaceous glands