The hair follicle barrier to involvement by malignant melanoma

Follicular colonization in melanocytic nevi and melanoma: A literature review

The lentiginous spread of melanocytes into the hair follicle can be observed in a number of benign melanocytic neoplasms such as in nevi but also in sun-induced melanocytic hyperplasia and melanoma. The follicular colonization by melanocytes in melanoma is classified into three distinct patterns: primary follicular melanoma, melanoma with folliculotropism, and invasive melanoma arising from melanoma in situ with folliculotropism. The role of follicular colonization in melanoma pathologic staging is still a matter of debate though the description of the latter has been recommended by the International Collaboration on Cancer Reporting. In this review, we will discuss the role of follicular colonization in melanoma and melanocytic nevi as well as the facts and controversies regarding this topic.

Loss of 'Epidermal Melanin Unit' Integrity in Human Skin During Melanoma-Genesis

Cutaneous melanoma can be a most challenging neoplasm of high lethality, in part due to its extreme heterogeneity and characteristic aggressive and invasive nature. Indeed, its moniker 'the great masquerader' reflects that not all melanomas are created equal in terms of their originating cellular contexts, but also that melanoma cells in the malignant tumor can adopt a wide range of different cell states and variable organotropism. In this review, we focus on the early phases of melanomagenesis by discussing how the originating pigment cell of the melanocyte lineage can be influenced to embark on a wide range of tumor fates with distinctive microanatomical pathways. In particular, we assess how cells of the melanocyte lineage can differ by maturation status (stem cell; melanoblast; transiently amplifying cell; differentiated; post-mitotic; terminally-differentiated) as well as by micro-environmental niche (in the stratum basale of the epidermis; within skin appendages like hair follicle, eccrine gland, etc). We discuss how the above variable contexts may influence the susceptibility of the epidermal-melanin unit (EMU) to become unstable, which may presage cutaneous melanoma development. We also assess how unique features of follicular-melanin unit(s) (FMUs) can, by contrast, protect melanocytes from melanomagenesis. Lastly, we postulate how variable melanocyte fates in vitiligo, albinism, psoriasis, and alopecia areata may provide new insights into immune-/non immune-mediated outcomes for melanocytes in cutaneous melanin units.

Cutaneous and Mucosal Melanomas of Uncommon Sites: Where Do We Stand Now?

Melanomas arising at uncommon sites include a group of lesions related to unusual localizations in specific ethnic groups. The rarity of the disease often represents a limit to the participation of patients in specific trials. However, this peculiar genetic scenario has important therapeutic implications regarding new oncologic therapies. The aim of this article is to review the clinical features, somatic alterations and therapeutic options for melanomas of uncommon sites. They can be classified as cutaneous and mucosal lesions affecting the nail apparatus, palms/soles, oral mucosa, genital area and scalp. The prognosis may be worse compared to melanomas of other districts, and a prompt diagnosis may dramatically influence the outcome. Dermatologists and oncologists should therefore distinguish this melanoma subgroup in terms of surgical intervention and medical treatment. Due to the lack of mutations in genes usually found in cutaneous melanomas, the discovery of novel targets is required to develop new strategies and to change the prognosis of non-responders or wild-type patients.

Syringotropic Melanoma: A Diagnostic Challenge With Prognostic Implications

The presence of neoplastic melanocytes within the eccrine apparatus into the reticular dermis and/or subcutaneous tissue is extremely rare. The staging of syringotropic melanomas and their biological behavior are still controversial. We present 6 new cases of syringotropic melanoma and their main histopathologic features; review the previous literature; and discuss about the origin, staging, and prognosis of this rare variant of melanoma.

Folliculotropism in head and neck lentigo maligna and lentigo maligna melanoma

BACKGROUND

Lentigo maligna (LM) and lentigo maligna-melanoma (LMM) are histotypes of melanoma arising in skin with cumulative solar radiation damage. The extension of atypical melanocytes to the hair follicle (folliculotropism) is a histopathological feature of LM/LMM. Its role has not been totally clarified, but it may be correlated to treatment response in LM or to progression in LMM.

OBJECTIVE

This retrospective, multicentric study aims to identify dermatoscopic features associated with folliculotropism in LMs/LMMs.

PATIENTS AND METHODS

We analyzed cases of head and neck LMs/LMMs diagnosed between 2005-2014 at Melanoma Units, University of Bologna/Modena/Florence/Siena (Italy), Nice (France): 25 LMs and 73 LMMs were included.

RESULTS

Grey circles (44 %) indicated an isthmic/bulb level of involvement, which were completely absent in the infundibular LM lesions (P = 0.041). In the group of LMMs, light/dark brown pseudonetwork and light brown structureless areas were an indicator of diffuse distribution of malignant melanocytes in the follicular units (P < 0.001 and P = 0.001, respectively), while grey circles indicated focal or diffuse distribution (P < 0.001).

CONCLUSIONS

A better understanding of the extension of malignant melanocytes is helpful, aiding clinicians in their decision to perform a radical excision or obtaining a biopsy in the most invasive area of the lesion, which includes potential folliculotropism.

Hair(y) Matters in Melanoma Biology

Melanocyte stem cells (MeSCs), one candidate for the cellular origin of melanoma, reside in the bulge region of the hair follicle (HF), an immune-privileged tissue niche with impaired tumor immunosurveillance. Surprisingly, however, primary melanoma is only very rarely associated with HFs. Here, we explore the hypothesis that this profoundly immunoinhibitory signaling environment deprives both MeSCs and melanocytes of the anagen hair matrix of proinflammatory signals required for full oncogenic transformation. Understanding the cellular and molecular mechanisms for generating a putative antimelanoma tissue habitat, namely in the bulge, could help to recreate a similar melanoma-suppressive signaling environment in melanoma high-risk individuals. We further discuss how mimicking the bulge immune privilege may be an effective melanoma prevention strategy.

Malignant Melanoma Cells and Hair Follicles

OBJECTIVES

The extension of atypical melanocytes to the hair follicle, also termed melanoma folliculotropism, is poorly evaluated and its role is contradictory. We performed an observational study focusing on anatomical areas rich in follicles, such as the head and neck region.

METHODS

Primary head and neck melanomas diagnosed in the Melanoma Unit, Policlinic Sant'Orsola-Malpighi, University of Bologna were analyzed. Folliculotropism was evaluated with a quantitative and morphologic parameter. Statistical analyses were performed correlating patients' prognosis with folliculotropism and other clinical and histopathologic factors.

RESULTS

The study was carried out on a sample of 62 patients. The diffuse distribution (atypical melanocytes present in more than three contiguous follicular units) correlated with scalp localization, nodular subtype, higher Breslow thickness, and a poorer prognosis.

CONCLUSIONS

We believe that folliculotropism should be further investigated and reported by pathologists during the histologic diagnosis of melanoma.

mirTime: identifying condition-specific targets of microRNA in time-series transcript data using Gaussian process model and spherical vector clustering

Background

MicroRNAs, small noncoding RNAs, are conserved in many species, and they are key regulators that mediate post-transcriptional gene silencing. Since biologists cannot perform experiments for each of target genes of thousands of microRNAs in numerous specific conditions, prediction on microRNA target genes has been extensively investigated. A general framework is a two-step process of selecting target candidates based on sequence and binding energy features and then predicting targets based on negative correlation of microRNAs and their targets. However, there are few methods that are designed for target predictions using time-series gene expression data.

Results

In this article, we propose a new pipeline, mirTime, that predicts microRNA targets by integrating sequence features and time-series expression profiles in a specific experimental condition. The most important feature of mirTime is that it uses the Gaussian process regression model to measure data at unobserved or unpaired time points. In experiments with two datasets in different experimental conditions and cell types, condition-specific target modules reported in the original papers were successfully predicted with our pipeline. The context specificity of target modules was assessed with three (correlation-based, target gene-based and network-based) evaluation criteria. mirTime showed better performance than existing expression-based microRNA target prediction methods in all three criteria.

Availability and implementation

mirTime is available at https://github.com/mirTime/mirtime.

Supplementary information

Supplementary data are available at Bioinformatics online.

Follicular involvement is frequent in lentigo maligna: Implications for treatment

BACKGROUND

Follicular involvement of lentigo maligna (LM) is considered a histopathologic hallmark, but its prevalence and characteristics have not been well defined. The depth of intrafollicular extension by neoplastic melanocytes may have clinical importance in the treatment of LM.

OBJECTIVE

To describe the prevalence and features of follicular involvement in LM, including depth of follicular growth by melanocytes.

METHODS

A single-center retrospective study of 100 consecutive cases of surgically excised LM that was treated from 2013 to 2015. The slide review for cases with residual LM on the debulk specimen was performed by a dermatologic surgeon and dermatopathologist to characterize follicular involvement.

RESULTS

Of 100 specimens, 72 met the inclusion criteria for histopathologic evaluation. Follicular involvement was seen in 95.8% of specimens (95% confidence interval, 88.3%-99.1%), with a mean of 68% of follicles involved in a single specimen. The mean depth of intrafollicular growth by lesional melanocytes was 0.45 mm (standard deviation, 0.23; range, 0.1-1.1 mm). Tumor cells were confined to the infundibular portion of the hair follicle in 60.9% of specimens.

CONCLUSION

Superficial follicular involvement is a ubiquitous finding in LM. When treatment options for LM with a depth-dependent modality aiming for tumor clearance are being considered, mean and maximum depths of involvement should be taken into consideration.

Preoperative measurement of cutaneous melanoma and nevi thickness with photoacoustic imaging

Photoacoustic imaging (PAI) is an emerging biomedical imaging technology, which can potentially be used in the clinic to preoperatively measure melanoma thickness and guide biopsy depth and sample location. We recruited 27 patients with pigmented cutaneous lesions suspicious for melanoma to test the feasibility of a handheld linear-array photoacoustic probe in imaging lesion architecture and measuring tumor depth. The probe was assessed in terms of measurement accuracy, image quality, and ease of application. Photoacoustic scans included single wavelength, spectral unmixing, and three-dimensional (3-D) scans. The photoacoustically measured lesion thickness gave a high correlation with the histological thickness measured from resected surgical samples (r=0.99, P<0.001 for melanomas, r=0.98, P<0.001 for nevi). Thickness measurements were possible for 23 of 26 cases for nevi and all (6) cases for melanoma. Our results show that handheld, linear-array PAI is highly reliable in measuring cutaneous lesion thickness in vivo, and can potentially be used to inform biopsy procedure and improve patient management.

A systematic review on the role of imiquimod in lentigo maligna and lentigo maligna melanoma: need for standardization of treatment schedule and outcome measures

Lentigo maligna (LM) is an in situ variant of melanoma. Our objective was to systematically review clinical and histological clearance and recurrence rates of imiquimod treatment of LM with emphasis on progression to lentigo maligna melanoma (LMM). PubMed, EMBASE and the Cochrane library were searched from inception to May 2015. Articles were included if they described histologically proven LM treated with imiquimod 5% monotherapy or combined with another topical therapy. Analysed outcomes were clinical and histological clearance, recurrence rates and number of LMM. The quality was assessed using the GRADE-like checklist, and results were reported according to the PRISMA Statement. Twenty-six case reports, 11 retrospective studies, three prospective studies and one randomized controlled trial were included. One case report of poor quality was excluded. Complete clinical clearance was seen in 369 of 471 patients (78.3%). Histological clearance was present in 285 of 370 (77%) patients. LMM was diagnosed in nine (1.8%) patients 3.9 months (range 0-11 months) post-treatment. Univariate multinominal logistic regression showed that 6-7 applications/week had a 6.47 greater odds (P = 0.017) of resulting in complete clinical clearance compared to 1-4 applications/week. An intensity of 6-7 applications/week showed a 8.85 greater odds (P = 0.003) of resulting in histological clearance compared to 1-4 applications. Applying imiquimod >60 times during a treatment period of 12 weeks (range 4-36) showed a 7.75 greater odds (P = 0.001) of resulting in histological clearance compared to <60 total applications. In conclusion, a treatment schedule using imiquimod 6-7 applications per week, with at least 60 applications, shows the greatest odds of complete clinical and histological clearance of LM. Imiquimod is an option for patients unfit for or not willing to undergo surgery or radiotherapy. Nine cases of LM progressed to LMM shortly after treatment. Our hypothesis is that these LMM may have been present before starting imiquimod.

A proposed classification for follicular involvement by melanoma

BACKGROUND

Folliculotropism in melanoma is poorly characterized and standard categorization for follicular involvement by melanoma is unavailable. We propose a logical categorization system.

METHODS

We conducted a search of our archives over a 24-year period for cases mentioning the terms follicle, follicular, folliculotropic, folliculocentric and melanoma.

RESULTS

We identified 90 cases of melanoma with involvement of the hair follicle. Distinct patterns were identified. The invasive patterns were primary follicular, folliculotropic and invasive arising from melanoma in situ (MIS) with extensive follicular involvement. Follicular involvement by MIS was either lentiginous, nested or a combination of both. A total of 29 invasive melanomas were identified. Of these 12 had invasive melanoma around the hair follicle, 2 were primary follicular melanomas, 7 showed folliculotropism and 3 were invasive melanomas arising from MIS around the follicle. Seventeen invasive melanomas had follicles only involved by MIS (9 nested, 6 nested and lentiginous and 2 lentiginous). A total of 61 cases of MIS with follicular involvement were identified; of these 33 were lentiginous, 10 nested and 18 both lentiginous and nested.

CONCLUSION

We propose that the three distinct patterns of follicular involvement by invasive melanoma and the three distinct patterns of MIS will be valuable for logically categorizing involvement of the hair follicle by melanoma.

Lentigo maligna - anatomic location as a potential risk factor for recurrences after non-surgical treatment

Background

A higher incidence of lentigo maligna (LM) recurrences on the nose was previously observed in our cohort after non‐surgical treatment.

Objectives

To determine histological parameters that might be related to the previously observed higher incidence of LM recurrences on the nose after non‐surgical treatment.

Methods

We randomly selected 22 surgical specimens of LM on the nose and 22 on the cheek. Histopathological analysis was performed on haematoxylin and eosin stained and microphthalmia transcription factor immunohistochemically stained slides. The number of pilosebaceous units (PSU) per mm, maximum depth of atypical melanocytes along the skin appendages and maximum depth of the PSU itself were determined.

Results

The nose had a significantly higher density of PSU than the cheek. The atypical melanocytes extended deeper along the PSU on the nose with a mean (SD) depth of 1.29 mm (0.48) vs. a mean depth of 0.72 mm (0.30) on the cheek (P < 0.001). The maximum depth of the PSU on the nose was greater than on the cheek, mean (SD) depth of 2.28 mm (0.41) vs. 1.65 mm (0.82) (P = 0.003).

Conclusions

The higher recurrence risk of LM on the nose after non‐surgical treatment that we previously observed in our cohort is most likely based on a higher density of atypical melanocytes and also their deeper extension into the follicles. These results shed more light on our previous findings and learn that anatomical location is relevant for the risk of recurrence of LM after non‐surgical treatment.

Lentigo maligna mimicking invasive melanoma in Mohs surgery: a case report

Lentigo maligna is a lentiginous proliferation of atypical melanocytes confined to the epidermis, typically on chronically sun-damaged skin. Following biopsy and exclusion of invasive disease, therapy may involve Mohs surgery, topical treatment or radiotherapy. However, lentigo maligna often involves adnexal structures, creating histological difficulty in distinguishing these foci from invasive melanoma. We present a case in which, during Mohs excision, a nodule of severely atypical melanocytes appeared to lie within the dermis, potentially altering treatment and prognosis. The use of laminin-5 provided a means of resolving this diagnostic dilemma, facilitating continuation of Mohs surgery until tumour clearance was achieved.