Absence of Ochre Fluorescence in Acral Melanoma Under Ultraviolet Dermoscopy

Dear Editor,

1.

Ultraviolet‐induced fluorescence dermoscopy (UVFD) has emerged as a promising adjunctive imaging tool in skin cancer evaluation. Recently, a distinct feature described as “ochre fluorescence (OF)” has been identified under UVFD [1, 2]. Although OF has been proposed as a potential clue to melanoma, particularly invasive melanoma, recent evidence suggests that it may also occur in a small subset of benign melanocytic lesions and should therefore be interpreted in conjunction with conventional dermoscopy rather than as a standalone diagnostic criterion [2, 3]. The influence of anatomical site on this phenomenon remains unexplored. Acral skin, characterized by a thick stratum corneum and distinct adnexal architecture, may influence UV‐induced optical patterns. In this study, we aimed to evaluate the presence of OF in acral versus non‐acral melanomas to determine whether this phenomenon may be influenced by tumor‐related biologic factors or the anatomical microenvironment.

In this retrospective study conducted between January 2023 and March 2026 at a tertiary dermatology center, cases were identified from our melanoma archive based on the availability of adequate UVFD imaging and complete clinicopathological data. All eligible acral melanoma cases were included, while non‐acral melanomas from the same period were selected for comparative analysis. Images were acquired using a DL5 dermatoscope (DermLite, USA) in polarized, non‐polarized, and UVFD (365 nm) modes. A total of 44 histopathologically confirmed melanoma cases were included, comprising 20 acral (12 invasive, 8 in situ) and 24 non‐acral melanomas (23 invasive, 1 in situ). The mean patient age was 58.6 ± 18.5 years, with a slight female predominance (25 females, 19 males). Detailed clinicopathological characteristics and the presence of OF under UVFD are summarized in Table 1.

TABLE 1.

Clinicopathological characteristics and presence of ochre fluorescence under ultraviolet‐induced fluorescence dermoscopy (UVFD) in acral and non‐acral melanomas.

Feature	Non‐acral melanoma (n = 24)	Acral melanoma (n = 20)
Demographics
Mean age (years)	54.1 (range: 15–88)	63.0 (range: 24–93)
Male/Female ratio	11/13	8/12
Histopathological features
Invasive/In situ	23/1	12/8
Median Breslow, mm Interquartile range (IQR)	1.1 (range: 0.0–6.0) 0.7–1.6	2.3 (range: 0.0–7.5) 0.0–3.6
Ulceration, n (%)	5 (20.8%)	10 (50.0%)
UVFD
Ochre fluorescence, n (%)	10 (41.7%)	1 (5.0%)

Our results revealed a notable disparity: OF was observed in 41.7% (10/24) of non‐acral melanomas but in only 5.0% (1/20) of acral melanomas (p = 0.006). Non‐acral melanomas were more likely to exhibit this feature (OR = 13.6). Notably, OF was exclusively observed in invasive melanomas; none of the nine in situ cases in our cohort demonstrated this pattern. The only acral case exhibiting OF was located at the Wallace line, the transitional zone between glabrous and non‐glabrous skin. This site‐dependent behavior is further highlighted in Figure 1 and in the Supporting Informations (Mendeley Figures S1–S3 available via DOI: 10.17632/pwdx6wr2df.2).

FIGURE 1.

Comparison of ultraviolet‐induced fluorescence dermoscopy (UVFD) patterns. (a, b) Non‐acral melanoma (Breslow thickness 1.2 mm, mitotic rate 4/mm², no ulceration, no regression, and no perineural or perivascular invasion) on the dorsal hand showing prominent ochre fluorescence under UVFD. (c, d) Acral melanoma (Breslow thickness 7.0 mm, ulceration present, mitotic rate 13/mm², no regression, and no perineural or perivascular invasion) on the plantar surface showing complete absence of ochre fluorescence despite advanced tumor features.

The biochemical origin of OF remains uncertain, with proposed mechanisms including the accumulation of lipofuscin, porphyrins, and melanin‐related oxidative byproducts [1].

Our findings suggest that the local skin architecture plays an important role in modulating this fluorescence. Acral skin is characterized by a markedly thickened stratum corneum, compact orthokeratosis, and a unique surface topography with pronounced dermatoglyphics [4]. These features may act as an optical barrier, attenuating or scattering ultraviolet‐induced emission signals and thereby masking underlying fluorescence. Furthermore, the absence of sebaceous glands and the unique eccrine‐gland‐dominant environment of acral sites might alter local pH or metabolic pathways responsible for generating fluorescent metabolites. In addition, chronic mechanical pressure and friction may also contribute to the altered fluorescence patterns. Similar to mechanisms proposed for fluorescence changes in inflammatory dermatoses such as psoriasis, mechanical stress may modify epidermal optical properties and influence the penetration or emission of UV‐induced fluorescence signals.

Beyond structural differences, acral melanomas are biologically distinct from their non‐acral counterparts [5]. In our cohort, all tested acral cases were BRAF‐negative, harboring mutations in c‐KIT, NRAS, or NF1, whereas non‐acral cases frequently demonstrated BRAF and TERT mutations. Although no direct relationship between specific mutations and OF was established, these findings raise the possibility that OF may reflect metabolic characteristics linked to distinct oncogenic pathways.

This study has several limitations, including its retrospective design, relatively small sample size, and uncertain biochemical basis of OF. The unequal distribution of melanoma in situ and invasive lesions between groups, together with the limited number of invasive acral melanomas, warrants cautious interpretation, particularly because OF has been reported only in a subset of invasive melanomas. In addition, UVFD is susceptible to artifacts. Although patients were questioned regarding topical agent use before imaging, unrecognized fluorescence‐altering substances cannot be fully excluded. Larger prospective studies are needed to clarify whether the observed differences reflect anatomical, optical, or biological variation.

Funding

The authors have nothing to report.

Consent

The authors obtained consent for the publication of recognizable patient photographs or other identifiable material at the time of article submission to the journal, stating that all patients gave consent with the understanding that this information may be publicly available. This study was approved by the local Ethics Committee (approval number: I05‐424‐25).

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.