Rare presentations of primary melanoma and special populations: a systematic review

Interaction between Age and Primary Site on Survival Outcomes in Primary GI Melanoma over the Past Decade

BACKGROUND

Primary malignant melanomas of the Gastrointestinal mucosa are uncommon. Most cases of gastrointestinal (GI) melanomas are secondary, arising from metastasis at distant sites. The purpose of this study is to assess to what extent the interaction between independent prognostic factors (age and tumor site) of primary GI melanoma influence survival. Furthermore, we also aimed to investigate the clinical characteristics, survival outcomes, and independent prognostic factors of patients with primary GI melanoma in the past decade.

METHODS

A total of 399 patients diagnosed with primary GI melanoma, between 2008 and 2017, were enrolled in our study by retrieving data from the Surveillance, Epidemiology, and End Results (SEER) database. We analyzed demographics, clinical characteristics, and overall mortality (OM) as well as cancer-specific mortality (CSM) of primary GI melanoma. Variables with a p value < 0.1 in the univariate Cox regression were incorporated into the multivariate Cox model (model 1) to determine the independent prognostic factors, with a hazard ratio (HR) of greater than 1 representing adverse prognostic factors. Furthermore, we analyzed the effect of the interaction between age and primary location on mortality (model 2).

RESULTS

Multivariate cox proportional hazard regression analyses revealed higher OM in age group 80+ (HR = 5.653, 95% CI 2.212-14.445, p = 0), stomach location of the tumor (HR = 2.821, 95% CI 1.265-6.292, p = 0.011), regional lymph node involvement only (HR = 1.664, 95% CI 1.051-2.635, p < 0.05), regional involvement by both direct extension and lymph node involvement (HR = 1.755, 95% CI 1.047-2.943, p < 0.05) and distant metastases (HR = 4.491, 95% CI 3.115-6.476, p = 0), whereas the lowest OM was observed in patients with small intestine melanoma (HR = 0.383, 95% CI 0.173-0.846, p < 0.05). Multivariate cox proportional hazard regression analyses of CSM also revealed higher mortality of the same groups and lower CSM in small intestine and colon melanoma excluding the rectum. For model 2, considering the interaction between age and primary site on mortality, higher OM was found in age group 80+, followed by age group 40-59 then age group 60-79, regional lymph node involvement only, regional involvement by both direct extension and lymph node involvement and distant metastases. The small intestine had a lower OM. The rectum as primary location and the age range 40-59 interacted to lower the OM (HR = 0.14, 95% CI 0.02-0.89, p = 0.038). Age and primary gastric location did not interact to affect the OM. For the CSM, taking into account the interaction between age and the primary location, higher mortality was found in the same groups and the colon location. The primary colon location also interacted with the age group 40-59 to increase the CSM (HR = 1.38 × 10⁹, 95% CI 7.80 × 10⁷-2.45 × 10¹⁰, p = 0).

CONCLUSIONS

In this United States population-based retrospective cohort study using the SEER database, we found that only the age range 40-59 interacted with the rectum and colon to lower and increase mortality respectively. Primary gastric location, which was the single most important location to affect mortality, did not interact with any age range to influence mortality. With those results, we hope to shed some light on this rare pathology with a very dismal prognosis.

Classification and Staging of Melanoma in the Head and Neck

The rates of melanoma continue to rise, with recent estimates have shown that 18% to 22% of new melanoma cases occur within the head and neck in the United States each year. The mainstay of treatment of nonmetastatic primary melanomas of the head and neck includes the surgical resection and management of regional disease as indicated. Thorough knowledge of the classification and staging of melanoma is paramount to evaluate prognosis, determine the appropriate surgical intervention, and assess eligibility for adjuvant therapy and clinic trials. The traditional clinicopathologic classification of melanoma is based on morphologic aspects of the growth phase and distinguishes 4 of the most common subtypes as defined by the World Health Organization: superficial spreading, nodular, acral lentiginous, and lentigo maligna melanoma. The data used to derive the AJCC TNM Categories are based on superficial spreading melanoma and nodular subtypes. Melanoma is diagnosed histopathologically following initial biopsy that will assist with classifying the tumor to guide treatment. Classification is based on tumor thickness and ulceration (T stage, Breslow Staging), Regional Lymph Node Involvement (N Stage), and presence of metastasis (M Stage). Tumor thickness (Breslow thickness) and ulceration are 2 independent prognostic factors that have been shown to be the strongest predictors of survival and outcome. Clark level of invasion and mitotic rate are no longer incorporated into the current AJCC staging system, but still have shown to be important prognostic factors for cutaneous melanoma. For patients with metastatic (Stage IV) disease Lactate Dehydrogenase remains an independent predictor of survival. The Maxillofacial surgeon must remain up to date on the most current management strategies in this patient population. Classification systems and staging provide the foundation for clinical decision making and prognostication for the Maxillofacial surgeon when caring for these patients.

Subungual melanoma with blue naevus-like morphological features: a clinicopathological retrospective analysis of nine cases

Melanocytic lesions in the nail apparatus are often challenging. Both subungual melanomas (SUM) and blue naevus of the nail are very rare. Occasionally, melanomas may mimic blue naevus histologically. Benign and malignant blue melanocytic lesions are commonly associated with G protein mutations, a distinct abnormality not associated with conventional subungual melanomas. We describe the clinical, histological and immunohistochemical features of nine cases of SUM with blue naevus-like morphological features. Mutations in exon 4 and 5 of GNAQ and GNA11 were investigated in two cases, which showed no mutations. RNA-seq of one case revealed unknown mutations along with mutations in ATM, METK and ARID1A. Our study delineates a variant of SUM that mimics blue naevus. Awareness of this pitfall is important when evaluating heavily pigmented lesions around the nail in order to avoid misdiagnosis. Appropriate sampling of subungual lesions and clinicopathological correlation are paramount to reach the correct diagnosis.

Pure and Mixed Desmoplastic Melanomas: A Retrospective Clinicopathologic Comparison of 33 Cases

BACKGROUND

Pure and mixed desmoplastic melanomas (DMs) may have different natural histories and behaviors.

METHODS

We conducted a retrospective review of patients diagnosed with DM at our institution between January 1997 and April 2019. A total of 33 unique DMs were identified and subsequently analyzed based on the histologic type (pure vs. mixed).

RESULTS

The majority (57.6%) of our cases were classified as pure histology. Patients with pure DMs were more likely to be men (P = 0.035) and be older than 65 years (P = 0.019) compared with patients with mixed DMs. Patients with mixed DM were more likely to have mitoses present (P = 0.001) compared with patients with pure DM. There were no differences in ulceration, perineural invasion, vascular invasion, or survival between patients with pure and mixed histologic subtypes. In addition, no differences in sentinel lymph node biopsy, radiation, or chemotherapy were noted between the 2 histologic subtypes. Immunohistochemistry showed that 27.3% of the pure DMs stained with Melan-A and HMB45 were positive for these immunomarkers.

CONCLUSIONS

Pure and mixed variants of DM were found to have similar clinicopathologic characteristics. Patients with the mixed histologic subtype were more likely to have mitoses, but no difference in the therapeutic management or patient survival was seen between the 2 subtypes.

Primary melanoma of the anorectal region: clinical and histopathological review of 17 cases. A retrospective cohort study

AIM

The aim of our study was to scrutinize diagnostic and treatment factors that may contribute to the low survival rate from anorectal melanoma while adding 17 more cases to the global research database.

METHOD

We carried out a retrospective analysis of 17 cases of anorectal melanoma treated at a single institution from 2000 to 2020. Data on patient age, sex, complaints, treatment and survival as well as tumour size, resection margins, histological and immunohistochemical features were assessed.

RESULTS

The median age of patients was 72 ± 12.49 (45-92) years. Most of the patients were women (n = 11, 64.71%). Three (17.65%) patients underwent no radical treatment. Of eight patients treated initially with radical surgery (either total mesorectal excision or abdominoperineal resection), six (75%) were found to have positive lymph nodes. Mean survival was 20 ± 23.46 (1-84) months. The average diameter of the resected tumours was 5.43 ± 3.02 cm (1.3-10 cm). Most tumours had epithelioid or spindle cell morphology and were positive for one or more melanocytic markers (S100, HMB-45 or MITF). More than half of the tumours contained no or very little melanin pigment. None of the tumours had significant lymphocytic infiltration. Three tumours showed positivity for keratins (PANCK or CAM5.2) and one tumour showed positivity for C-KIT stain.

CONCLUSION

An aggressive surgical approach may have an effect on survival in most early stages while more advanced disease benefits from a more conservative approach. Attention to sentinel lymph nodes and further systemic research into therapy is required. For now, treatment and diagnostic modalities seem to be inconsistent, requiring further investigation to elucidate common points.

Mucosal Melanoma

Mucosal melanoma is a rare but aggressive cancer arising in mucosal surfaces most commonly in the head and neck. The clinical presentation is often nonspecific and differs in relation to the site of origin so often diagnosis is delayed resulting in poor prognosis. Mucosal melanoma has a 5-year survival of only 25%. Surgery with negative margins is the mainstay of treatment but dependent on several variables including anatomic location, involved structures, and size of tumor. Although not well defined given the rarity of mucosal melanoma, there is a role for radiation and systemic therapy in the treatment of this disease.

The challenge of primary gastric melanoma: a systematic review

AIM

Primary gastric melanoma is a rare clinical presentation. The purpose of this review was to compare the 1-year survival in patients who underwent surgery with patients who did not receive treatment.

PATIENTS & METHODS

A systematic search of databases for case reports and case series of primary gastric melanoma was conducted.

RESULTS

The mean survival of patients was 22 months. One-year survival was 56.5% with surgery, rising to 66% with adjuvant therapy. Mean survival of the surgical group was 21.05 months (±20.2) versus 4.5 months (±3.61) in the nonsurgical group.

CONCLUSION

Primary gastric melanoma has a poor prognosis but early surgical intervention can have a significant impact on patient outcome. We reviewed the biology and clinical diagnosis of gastrointestinal melanoma and the current management options available.

Clinicopathological Features and Prognostic Factors of Primary Acral Melanomas in Caucasians

Background: Cutaneous melanomas located on the acral part of extremities (hand and foot melanoma; HFM) comprise a rare group within all melanomas in Caucasians. HFM is associated with a poor prognosis. We aimed to evaluate clinicopathological features, long-term outcomes, and prognostic factors in primary HFM in Caucasians. Methods: Medical records of all consecutive patients treated between 1997 and 2014 were revised. Patients were diagnosed with primary cutaneous melanoma at I-II clinical stage, and sentinel lymph node biopsy was conducted. The analysis was performed to define the clinicopathological factors influencing outcomes in the HFM and subungual cohort. Among 2537 consecutive patients diagnosed with primary cutaneous melanoma, 247 cases of HFM (9.7%) were found, with a median follow-up time of 7.8 years. Results: Median primary tumor Breslow thickness in subungual melanomas and HFMs was 4.0 mm and 3.3 mm, respectively, significantly higher than in the entire population (median 2.2 mm; p < 0.01). In the HFM group, 37.6% of tumors were ulcerated. Metastases to sentinel lymph node (SLN) were found in 28.3% of HFMs. The 10-year overall survival rate in the HFM group and subungual melanomas was 48.1% and 49.3%, respectively, compared to 63.0% in non-HFM melanomas. Conclusions: Our results confirm that patients with HFMs display worse overall survival compared to the entire melanoma population, with male gender and positive SLN biopsy status acting as independent negative prognostic factors.

Mutation profile of primary subungual melanomas in Caucasians

Background: Specific genomic profile of cutaneous melanomas is related to UVR exposure, which exerts biological and therapeutic impact. Subungual melanoma (SUM) is an exceedingly rare disease; therefore, it is not well characterized. SUM pathogenesis is not related to UVR induced DNA damage and expected to differ from other melanoma subtypes. Our study aimed to define the mutation profile of SUM in Caucasians.

Materials and Methods: Next-generation sequencing-based genomic analysis was used to identify frequently mutated loci in 50 cancer-related genes in 31 SUM primary tumors.

Results: The most abundant mutations in SUM were found in KIT – in 13% of cases and NRAS – also in 13%, while BRAF - only in 3% of cases.

Conclusions: Our findings confirmed a high frequency of KIT and NRAS mutations in SUM, as well as a low incidence of BRAF mutations. We reported novel KRAS, CTNNB1, TP53, ERBB2, and SMAD4 mutations in SUM. Our findings provide new insights into the molecular pathogenesis of SUM.

Gastrointestinal involvement of primary skin diseases

Less is known about gastrointestinal (GI) involvement of primary skin diseases due to the difference in embryology, histology, microbiology and physiology between integument and alimentary tract. Oesophagus, following the oropharyngeal mucosa, is the most common GI segment affected by primary skin diseases, especially by eosinophilic oesophagitis, lichen planus and autoimmune bullous dermatoses like pemphigus vulgaris, mucosal membrane pemphigoid and epidermolysis bullosa acquisita. Eosinophilic oesophagitis is an emerging chronic atopic disease with oesophageal dysfunction as the typical presentation, and oesophageal narrowing, rings and stricture as late complications. Oesophageal lichen planus mainly involves the proximal to mid-oesophagus in elderly aged women with long-term oral mucosal lesions. In acute attack of pemphigus vulgaris, oesophageal involvement is not uncommon but often neglected and may cause sloughing oesophagitis (oesophagitis dissecans superficialis) with acute GI bleeding in rare cases. GI manifestation of hereditary bradykininergic angio-oedema with colicky acute abdomen mostly affects small intestine, usually in the absence of pruritus or urticaria, and is more severe and long-lasting than the acquired histaminergic form. Strong evidence supports association between inflammatory bowel disease, especially Crohn disease, and hidradenitis suppurativa/acne inversa. Patients with vitiligo need surveillance of autoimmune liver disease, autoimmune atrophic gastritis or coeliac disease when corresponding symptoms become suspect. Melanoma is the most common primary tumour metastatic to the GI tract, with small intestine predominantly targeted. Gastrointestinal involvement is not uncommon in disseminated mycosis fungoides. Extramammary Paget's disease is an intraepidermal adenocarcinoma of controversial origin, and a high association between the anogenital occurrence and colorectal adenocarcinoma has been reported. As GI tract is the largest organ system with multidimensional functions, dermatologists in daily practice should be aware of the gastrointestinal morbidities related to primary skin diseases for an early diagnosis and treatment.

Combination therapy improves immune response and prognosis in patients with advanced oral mucosal melanoma: A clinical treatment success

OBJECTIVE

This study was undertaken to analyze disease response and immune response to assess treatment effectiveness and success in patients with advanced oral mucosal melanoma treated with cytokines injection, cryosurgery, and adoptive cell transfer therapy.

STUDY DESIGN

Ten patients were enrolled in the study, and the relevant characteristics and immunologic differences were evaluated.

RESULTS

All patients achieved an objective clinical response according to the Response Evaluation Criteria in Solid Tumors, including 7 cases of continuing complete remission (55, 27, 87 + , 58⁺, 58 + , 45 + , and 37 + months) and 3 cases of partial remission (30, 12, and 9 months). Five responders are currently alive. After combination therapy, we observed that the proportion of CD3+ lymphocytes and the secretion of interferon-γ increased, whereas interleukin-10 decreased. In the assay of improved cytokine-induced killer cells, CD4+CD25+ regulatory T cells declined, and natural killer cells upregulated. Meanwhile, the proliferation rate of in vitro cultured improved cytokine-induced killer cells improved after courses of therapy.

CONCLUSIONS

Combination therapy of cytokine injection, cryosurgery, and transfer of improved cytokine-induced killer cells may be a promising approach for patients with oral mucosal melanoma.

Morphologic and Immunohistochemical Characteristics of Anorectal Melanoma

Anorectal melanoma is a rare aggressive disease. Due to its rarity and considerable histologic and immunohistochemical variabilities, misdiagnosis as lymphoma, carcinoma, sarcoma, and/or gastrointestinal stromal tumor is not uncommon, particularly in amelanotic cases. We reviewed histologic features and immunohistochemical stains of 19 anorectal melanoma cases. Histopathologic features were evaluated including junctional activity, melanin pigment, and morphologic features. Immunohistochemical stains were performed using Sox10, S100 protein, HMB-45, melan-A, CD56, and cytokeratins. Epithelioid histopathologic morphology was observed in 63.2% of the cases followed by 47.4% of the cases with spindle-cell, 26.3% with lymphoma-like, and 26.3% with pleomorphic morphologies. Junctional melanocytic activity was seen in almost half of the cases. Melanin pigment was absent (amelanotic) in nearly 40% of the cases. Immunohistochemically, diffuse positive expression of Sox10, S100 protein, melan-A, and HMB-45 was seen in 100%, 40%, 53.3%, and 38.5% of the cases, respectively. Cytokeratins were negative and CD56 was positive in 2 cases. These findings indicate that anorectal melanomas often show one or combined histolopathologic features without presence of melanin pigment and absence of junctional melanocytic activity. Anorectal melanoma should be kept in mind in the differential diagnosis of malignant neoplasms of anorectal region with epithelioid, spindle-cell, lymphoma-like, and pleomorphic morphologies. Sox10 immunohistochemistry stain can be used as a first-line screening tool to avoid extensive or unnecessary workups and/or potential misdiagnosis.

Mucosal Melanoma: a Literature Review

PURPOSE OF REVIEW

Mucosal melanoma is of great interest due to its aggressive behavior and less favorable prognosis. The literature is mainly case reports and case series. Here, we will collect the knowledge on mucosal melanoma from the last decade and review the literature. The main focus is being site-specific clinical features, treatment, and prognosis.

RECENT FINDINGS

The use of immunotherapy gain ground as for others subsets of melanoma. Anti-CTLA-4 and anti-PD-1/ PD-L1 blockade in mucosal melanoma have been evaluated in recent studies. Clinical trials are ongoing. The etiology of mucosal melanomas remains unknown. Head and neck mucosal melanomas are most common. Wide excision surgery is the treatment of choice. The effect of adjuvant therapy on survival remains questionable due to the limited knowledge. Radiotherapy seems to give better local control. The overall five-year survival rate for mucosal melanomas is 0-45%. Recent data indicates that this may be improved by the immunotherapy in the years to come.

The use of pembrolizumab for the treatment of metastatic uveal melanoma

Uveal melanoma is a rare type of melanoma, with only five to seven cases per one million persons diagnosed each year. Patients with metastatic melanoma of uveal origin tend to have lower response rates on traditional therapies. Herein we report our experience with 10 patients with metastatic uveal melanoma (MUM) who received pembrolizumab. Eligible patients were more than or equal to 18 years old, had unresectable MUM, progressed on prior ipilimumab therapy, had good performance status (Eastern Cooperative Oncology Group of 0 or 1), and adequate organ and marrow function. Patients could have central nervous system disease, but needed to be clinically stable. Patients were treated with 2 mg/kg pembrolizumab intravenously over 30 min every 3 weeks until disease progression, unacceptable toxicity, or for up to 2 years. Between April 2014 and October 2014, we treated a total of 10 patients with MUM with pembrolizumab. Median age was 65 years, with 70% being female. As of the data cutoff date of 14 May 2015, median progression-free survival was 18 weeks (range 3.14-49.3 weeks), with four patients still currently receiving therapy. Of eight evaluable patients, there was one complete response, two partial responses, and one patient with stable disease. Four patients had rapidly progressive disease. Toxicities were as expected and were usually grade 1/2 in nature. Although this cohort of patients was small, to our knowledge this is the first such report of outcomes in uveal melanoma patients being treated with anti-PD1 therapy. In the absence of a clinical trial, treatment with pembrolizumab appears to be a viable option for patients with MUM.

Rare and Extensive Malignant Melanoma of the Oral Cavity: Report of Two Cases

Primary oral melanomas are uncommon malignant neoplasm of melanocytes origin. The most common site of oral melanoma is maxillary gingiva and hard palate. Oral mucosal melanoma exhibit a pathobiological behavior and clinical features different from cutaneous melanomas. Oral melanomas are often clinically silent which may consequently result in delayed diagnosis; thus, making the prognosis extremely poor. This case report presents clinical, histopathological and immunohistochemical features of two cases of advanced oral melanoma, one pigmented or melanotic melanoma in a 46-year-old female and another amelanotic melanoma in a 59-year-old male patient, with chief complaint of swelling in oral mucosa. Most oral melanomas are usually asymptomatic lesions with quick growing. Thus, the most cases are detected in late stage of diagnosis. Early diagnosis with careful examination by dentists, and early biopsy of pigmented and suspicious non-pigmented lesions would have an imperative role in more survival rate and better prognosis.

A Review of the Aetiopathogenesis and Clinical and Histopathological Features of Oral Mucosal Melanoma

Oral mucosal melanoma is an uncommon, usually heavily melanin-pigmented, but occasionally amelanotic aggressive tumour with a poor prognosis. Despite radical surgery, radiotherapy, or chemotherapy, local recurrence and distant metastasis are frequent. Microscopical examination is essential for diagnosis, and routine histological staining must be supplemented by immunohistochemical studies. The aetiology is unknown, the pathogenesis is poorly understood, and the 5-year survival rate rarely exceeds 30%. In most cases, oral mucosal melanoma arises from epithelial melanocytes in the basal layer of the epithelium and less frequently from immature melanocytes arrested in the lamina propria. In both cases the melanocytes undergo malignant transformation, invade deeper tissues, and metastasize to regional lymph nodes and to distant sites. Very rarely metastasis from skin melanoma may give rise to oral mucosal melanoma that may be mistaken for primary oral mucosal melanoma. The pathogenesis of oral mucosal melanoma is complex involving multiple interactions between cytogenetic factors including dysregulation of the cKit signalling pathways, cell cycle, apoptosis, and cell-to-cell interactions on the one hand and melanin itself, melanin intermediates, and local microenvironmental agents regulating melanogenesis on the other hand. The detailed mechanisms that initiate the malignant transformation of oral melanocytes and thereafter sustain and promote the process of melanomagenesis are unknown.

Paediatric melanoma

Paediatric melanoma, although rare, is the most common skin cancer in children. Our current knowledge on paediatric melanoma incidence trends is expanding, as several studies have addressed this issue with conflicting results. Known risk factors for paediatric melanoma include family history of melanoma, a previous history of malignancy, large congenital nevi, numerous melanocytic nevi, sunburns, increased UV exposure and a sun-sensitive phenotype. In younger children, melanoma more often presents with atypical features, such as a changing, amelanotic or uniformly coloured, often bleeding lesion, not fulfilling in most cases the conventional ABCDE criteria. The major differential diagnoses are melanocytic nevi, proliferative nodules in congenital nevi and atypical Spitz tumours. Moreover, in the younger age group non-Caucasian children are over-represented, tumours tend to be thicker and lymph nodes are often involved. Despite the frequent diagnosis at an advanced stage, the overall survival is fair in paediatric melanoma. Specific guidelines for management of melanoma in children do not exist, and most often the disease is treated similarly to melanoma in adults.

Primary versus Metastatic Gastrointestinal Melanoma: A Rare Case and Review of Current Literature

Gastrointestinal (GI) melanomas are a rare diagnostic entity. Although there have been cases of melanomas solely in the GI tract, many debate their true origin: the gut versus a distant, undetected primary lesion that regressed known as melanoma of unknown primary. We present a case that involved diagnosing a GI melanoma and then backtracking to find a possible primary source. We review the most recent literature regarding possible etiologies of primary GI melanomas and how to differentiate whether it has a primary, metastatic, or unknown origin.

Oral mucosal melanoma: some pathobiological considerations and an illustrative report of a case

Oral mucosal melanoma is a relatively rare malignancy with an aggressive clinico-pathological behaviour. The mean 5-year survival rate is about 15 %. It arises primarily from melanocytes found in the basal cell layer of the epithelium, but may sometimes arise from melanocytes residing in the lamina propria. The pathogenesis is complex, and few of the molecular mechanisms underlying the development of oral mucosal melanoma have been defined. The extraneous risk factors associated with oral mucosal melanoma, if any, are unknown. Oral mucosal melanomas account for about 25 % of all mucosal melanomas of the head and neck, and exhibit a profile of cytogenetic alterations, and a pathobiological behaviour and clinical course different from that of cutaneous melanomas. As they are usually painless and grow quickly, as a rule, they are diagnosed late in the course of the disease when the lesions are already large and have metastasized to regional lymph nodes. In this paper we discuss some aspects of the pathobiology of oral mucosal melanoma, and present an illustrative case report.

Melanoma of the Hand: Current Practice and New Frontiers

Melanoma of the hand represents a complicated clinical entity. Anatomic features of the hand create challenges in successful management of melanoma not encountered elsewhere in the body. The objectives of this article are to outline current standards for managing melanoma of the hand including diagnosis, surgical, and chemotherapeutic management. Particular emphasis will be placed on currently debated topics of the role of sentinel lymph node biopsy, the role of Mohs micrographic surgery, tissue sparing management of subungual melanoma, and the consideration of melanoma of the hand as a distinct entity based on clinical and molecular studies.