Dermal squamo-melanocytic tumor: a unique biphenotypic neoplasm of uncertain biological potential

A Combined Spindle Cell Melanoma and Sarcomatoid Squamous Cell Carcinoma: A Rather Unique Squamomelanocytic Tumor

ABSTRACT

Squamomelanocytic tumor is a poorly defined term that indicates co-occurrence of malignant melanoma and squamous cell carcinoma within the same lesion. We present an unusual case of squamomelanocytic tumor in which both intermingling components showed predominantly spindle cell morphology and were confirmed with double staining for SOX-10 and AE1/AE3.

Two Squamomelanocytic Tumors With Dendritic Melanocytes: Thoughts About Origin

ABSTRACT

Cutaneous malignant squamomelanocytic tumor (SMT) is a rare neoplasm comprising 2 distinct cell populations of squamous cell carcinoma and a second component of either benign or malignant melanocytes. SMT most often presents as a keratotic papule in areas of chronic sun exposure, typically on the head or neck of middle-aged and elderly-aged, White male patient populations. In recent years, there has been an increase in case reports, including a review article published in 2023, identifying a total of 37 cases published in the literature. There are only 3 reported cases in the literature with spindled or dendritic cells in the melanocytic component, as most have been of the epithelioid subtype. Despite the increasing prevalence, the origin and pathophysiology is poorly understood. We report 2 cases of SMT with dendritic melanocytes that are centered around a hair follicle, proposing the theory that these 2 distinct cell types may arise from the hair follicles.

An enigmatic combined tumour of oral malignant melanoma and oral squamous cell carcinoma - A rare case report

Combined tumours are those composed of two benign tumours or a benign and malignant tumour or two malignant tumours occurring within the same tumour population. The incidence of combined tumours is very rare. Due to the rarity of these tumours, their biological behaviour remains unlashed. Incisional biopsy of a 48 years old female patient with single, diffuse tumour mass in the oral cavity showed combined tumour or collision tumour of malignant melanoma and squamous cell carcinoma. This was confirmed with immunohistochemistry study. The incidence of combined tumour of malignant melanoma and squamous cell carcinoma in oral cavity is extremely rare. To the best of our knowledge based on the previous literature records, this is the first case report of its kind where there is incidence in the human oral cavity.

Cutaneous Malignant Squamomelanocytic Tumor: A Case Report of a Rare Neoplasm

ABSTRACT

Cutaneous squamomelanocytic tumor (SMT) is an exceedingly rare cutaneous malignancy characterized by the presence of both squamous cell carcinoma and malignant melanoma within a single tumor. SMT typically presents clinically as keratotic skin papulonodules, most commonly occurring on the face, scalp, or other sun-exposed areas of middle-aged to elderly White male patients. Owing to the rare nature of this tumor, the histogenesis and prognosis remain relatively unclear. Histopathological examination of the tangential biopsy revealed an invasive cutaneous malignancy consisting of 2 distinct yet closely associated atypical cell populations: (1) a population of atypical squamoid epithelial cells arranged in cords and keratin pearls and (2) a population consisting of atypical, spindled cells with fine melanin pigment arranged in confluent sheets. Both populations of atypical cells emanated in an invasive pattern from the underside of the overlying epidermis into the deep dermis. Squamomelanocytic tumors are among the rarer types of collision tumors between 2 malignant lesions as most are basomelanocytic. For most reported SMTs, the melanoma population comprises epithelioid cell morphology, whereas our tumor is composed of spindled cell morphology. In this article, we exemplify a unique case of SMT in an 87-year-old male patient.

The clinicopathologic spectrum and genomic landscape of de-/trans-differentiated melanoma

Dedifferentiation and transdifferentiation are rare and only poorly understood phenomena in cutaneous melanoma. To study this disease more comprehensively we have retrieved 11 primary cutaneous melanomas from our pathology archives showing biphasic features characterized by a conventional melanoma and additional areas of de-/trans-differentiation as defined by a lack of immunohistochemical expression of all conventional melanocytic markers (S-100 protein, SOX10, Melan-A, and HMB-45). The clinical, histologic, and immunohistochemical findings were recorded and follow-up was obtained. The patients were mostly elderly (median: 81 years; range: 42-86 years) without significant gender predilection, and the sun-exposed skin of the head and neck area was most commonly affected. The tumors were deeply invasive with a mean depth of 7 mm (range: 4-80 mm). The dedifferentiated component showed atypical fibroxanthoma-like features in the majority of cases (7), while additional rhabdomyosarcomatous and epithelial transdifferentiation was noted histologically and/or immunohistochemically in two tumors each. The background conventional melanoma component was of desmoplastic (4), superficial spreading (3), nodular (2), lentigo maligna (1), or spindle cell (1) types. For the seven patients with available follow-up data (median follow-up period of 25 months; range: 8-36 months), two died from their disease, and three developed metastases. Next-generation sequencing of the cohort revealed somatic mutations of established melanoma drivers including mainly NF1 mutations (5) in the conventional component, which was also detected in the corresponding de-/trans-differentiated component. In summary, the diagnosis of primary cutaneous de-/trans-differentiated melanoma is challenging and depends on the morphologic identification of conventional melanoma. Molecular analysis is diagnostically helpful as the mutated gene profile is shared between the conventional and de-/trans-differentiated components. Importantly, de-/trans-differentiation does not appear to confer a more aggressive behavior.

A Wolf in Sheep's Clothing: Collision of Melanoma and Keratoacanthoma

Collision tumors consisting of melanoma and squamous cell carcinoma are very rare. We present the case of a deceptive hyperkeratotic nodule on the forearm of a 72-year-old woman, which clinically appeared to be a squamous cell carcinoma, keratoacanthoma type. Histological examination surprisingly revealed a coexisting epithelioid melanoma. Thus, this case report shows the importance of an early histopathological and immunohistochemical workup to prevent unnecessary diagnostic and therapeutic delay with negative effects on prognosis.

A rare case of invasive melanoma likely arising from passenger melanocytes of a basal cell carcinoma

Neoplasms consisting of different cell lineages within a single skin specimen are rare, yet well documented in the literature. However, to date, there appears to be no report of invasive melanoma arising directly from the passenger melanocytes of a basal cell carcinoma (BCC). We present a case of a 91-year-old male with a suspicious lesion on the ear. Histopathology and immunohistochemical staining revealed BCC closely intertwined with invasive melanoma that exhibited foci of chondroid differentiation. The melanoma appeared to arise from the benign-appearing passenger melanocytes of the BCC and lacked connection to the overlying epidermis or an in situ component. Multiple dermatopathologists reviewed the case and agreed that the most likely explanation for the histopathologic findings was that the invasive melanoma arose from the passenger melanocytes within the BCC.

Cutaneous neoplasms composed of melanoma and carcinoma: A rare but important diagnostic pitfall and review of the literature

We report two cases of combined cutaneous tumors composed of melanoma and carcinoma. The first tumor presented as a 5-mm pink-blue macule over the right zygomatic arch in an 85-year-old man. Shave biopsy and immunohistochemical studies revealed that the tumor was composed of melanoma (highlighted by SOX10 and MART-1, with high Ki-67 proliferative index) intermixed with nodular basal cell carcinoma (highlighted by pan-cytokeratin and Ber-EP4). The neoplastic melanocytes were confined to the basal cell carcinoma nodules, and a diagnosis of combined melanoma in situ and basal cell carcinoma was rendered. After therapeutic excision, the patient was disease-free at 9 months after the initial diagnosis. The second tumor presented as a 6-mm pink-brown crusted papule on the right forehead in an 89-year-old man. Shave biopsy and immunohistochemical studies revealed that the tumor was composed of malignant melanoma (MM) (highlighted by S100 and MART-1) intermixed with squamous cell carcinoma (SCC) (highlighted by cytokeratin and p63), and a diagnosis of combined MM-SCC was rendered. These two cases highlight the importance of recognizing these rare types of melanocytic-epithelial cutaneous neoplasms to arrive at an accurate diagnosis that may inform appropriate disease stage and therapy.

Uncommon Histopathological Variants of Malignant Melanoma: Part 1

Despite new horizons opened by recent advances in molecular pathology, histological evaluation still remains the diagnostic gold standard regarding cutaneous melanocytic neoplasms. Several histological variants of melanoma have been described, and their knowledge is crucial for accurate diagnosis and classification of cases with unusual clinicopathological features. Uncommon histological variants of melanoma have been described based on a broad constellation of features, including architectural pattern, stromal alterations, cytological attributes, and other morphological properties. This review is aimed at providing an extensive discussion of unusual but distinctive histopathological variants of melanoma.

Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (cSCC) is a malignant neoplasm of the skin characterized by an aberrant proliferation of keratinocytes. Cutaneous SCC is the second most common malignancy globally, and usually arises in the chronically sun-damaged skin of elderly white individuals. From a pathologist's perspective, it is important to differentiate cSCC from the benign and reactive squamoproliferative lesions and identify the high-risk features associated with aggressive tumor behavior. In this article, we provide an up-to-date overview of cSCC along with its precursor lesions and important histologic variants, with a particular emphasis on the histopathologic features and molecular pathogenesis.

Association of subungual melanoma and subungual squamous cell carcinoma: A case series

BACKGROUND

Subungual squamous cell carcinoma (SSCC) and subungual melanoma (SUM) are rare tumors. Several case reports of association of SSCC with SUM (SSCC-SUM) have been published.

OBJECTIVE

We sought to document the clinical, dermoscopic, and histologic features in a case series of SSCC-SUMs and describe their relative frequency compared with those of SSCC and SUM.

METHODS

All patients who underwent surgical exploration of the nail apparatus with a dermatopathologic examination from 2012 to 2015 were reviewed retrospectively to identify all cases of SSCC, SUM, and SSCC-SUM. For patients with SSCC-SUM, clinical characteristics were obtained from electronic medical records. All histologic specimens were reviewed by 3 dermatopathologists.

RESULTS

The medical records of 456 patients were reviewed. SSCC was diagnosed in 78 (17%), SUM was diagnosed in 63 (14%), and SSCC-SUM was diagnosed in 9. Patients with SSCC-SUM accounted for 11% of those with a diagnosis of SSCC (9 of 78) and 14% of those with a diagnosis of SUM (9 of 63).

LIMITATIONS

This was a single-institution retrospective study.

CONCLUSION

The association of SSCC and SUM is relatively frequent in patients with SUM and warrants further consideration to understand the underlying mechanisms involved.

Collision Tumour of Squamous Cell Carcinoma and Malignant Melanoma in the Oral Cavity of a Dog

A 7-year-old, male cocker spaniel was presented with a gingival proliferative lesion in the rostral maxilla and enlargement of the regional lymph node. Morphological and immunohistochemical analysis revealed a collision tumour composed of two malignant populations, epithelial and melanocytic, with metastasis of the neoplastic melanocytes to the regional lymph node. The epithelial component consisted of trabeculae and islands of well-differentiated squamous epithelium immunoreactive to cytokeratins. The melanocytic component had a varying degree of pigmentation of polygonal and spindle-shaped cells, growing in nests or densely packed aggregates and immunolabelled with S100, melanoma-associated antigen (melan A), neuron-specific enolase and vimentin antibodies. Protein markers involved in tumorigenesis or cell proliferation (i.e. COX-2, p53, c-kit and Ki67), were overexpressed by the neoplastic cells. To the authors' knowledge, this is the first description of an oral collision tumour involving malignant melanoma and squamous cell carcinoma in the dog.

Conjunctival Melanoma With Morphologic Diversity and Orbital Invasion

A 68-year-old male with a previous history of 3 dysplastic skin nevi was referred to ophthalmology for a 1-year history of a progressive growth of a firm nodule in the lower left eyelid. Examination revealed a firm nodule in the inferior anterior orbit and mild conjunctival pigmentation on the left inferior fornix. A conjunctival incisional biopsy was taken, showing a melanoma. Because of the infiltration by the mass of the orbit on magnetic resonance imaging, an exenteration was performed. Histopathological analysis showed a unique conjunctival melanoma showing morphological diversity; specifically, a pattern characteristic of conjunctival melanoma, and the concurrent presence of staghorn patterns, signet-ring cells, and rosettoid patterns. Seven years of follow-up shows that the patient is alive with no further metastasis or recurrence. This report represents the first documented case of multiple morphologic patterns within a conjunctival melanoma.

Tumor with the features of both squamous cell carcinoma and melanoma (melanocarcinoma)

Combined tumors of malignant melanoma (MM) and squamous cell carcinoma (SCC) are extremely rare and have unknown biological potential. Different theories of their development, including collision and dual/divergent differentiation, are proposed. Although some observations suggest an indolent course for such tumors, a case of MM metastasis was reported in a patient who initially presented with a combined MM-SCC tumor. Re-excisions of such tumors may show MM in situ and should be treated accordingly. Herein we present another case of a combined MM-SCC tumor in a 78 male patient with lentigo maligna seen after complete re-excision of the tumor.

[Dermoscopy of nails]

Pigmented and nonpigmented nail abnormalities often represent a challenge for clinicians because many, and sometimes potentially life-threatening differential diagnoses must be taken into consideration. Although many details of nail diseases can already be assessed with the naked eye, dermoscopy opens up a second microscopic level of inspection, which can be very useful for the diagnostic process. In the last 20 years dermoscopy has made rapid progress in the further development of criteria for the early recognition of melanoma. In addition, the use of dermoscopy has been extended to the examination of cutaneous adnexa, such as hairs (trichoscopy) and nails (onychoscopy). Many, sometimes highly specific criteria for the dermoscopic assessment of nail diseases have been described in a series of recently published articles. This review article provides important diagnostic aids for a well-founded dermoscopic assessment of nail diseases.

When all you have is a dermatoscope- start looking at the nails

Pigmented and non-pigmented nail alterations are a frequent challenge for dermatologists. A profound knowledge of clinical and dermatoscopic features of nail disorders is crucial because a range of differential diagnoses and even potentially life-threatening diseases are possible underlying causes. Nail matrix melanocytes of unaffected individuals are in a dormant state, and, therefore, fingernails and toenails physiologically are non-pigmented. The formation of continuous, longitudinal pigmented streaks (longitudinal melanonychia) may either be caused by a benign activation of matrix melanocytes (e.g., as a result of trauma, inflammation, or adverse drug reactions) or by a true melanocytic proliferation (e.g., in a nevus or melanoma). In general, non-continuous nail alterations, affecting only limited parts of the nail apparatus, are most frequently of non-melanocytic origin. Important and common differential diagnoses in these cases are subungual hemorrhage or onychomycosis. In addition, foreign bodies, bacterial infections, traumatic injuries, or artificial discolorations of the nail unit may less frequently cause non-continuous nail alterations. Many systemic diseases that may also show involvement of the nails (e.g., psoriasis, atopic dermatitis, lichen planus, alopecia areata) tend to induce alterations in numerous if not all nails of the hands and feet. A similar extensive and generalized alteration of nails has been reported after treatment with a number of systemic drugs, especially antibiotics and cytostatics. Benign or malignant neoplasms that may also affect the nail unit include glomus tumor, Bowen's disease, squamous cell carcinoma, and rare collision tumors. This review aims to assist clinicians in correctly evaluating and diagnosing nail disorders with the help of dermatoscopy.

Malignant melanoma within squamous cell carcinoma and basal cell carcinoma: is it a combined or collision tumor?--a case report and review of the literature

We report a case of a very unusual combined and collision basosquamous melanocytic malignant tumor on the chest of an 84-year-old man. To our knowledge, this is the first case report describing this entity. We attempt to address the diagnostic challenge and the clinical and histological characteristics of these rare neoplasms with a review of the English literature to further categorize and summarize what has been previously reported about these extraordinary tumors.

An uncommon malignant cutaneous squamomelanocytic tumor

The intermingling of two malignant neoplasms within the same cutaneous tumor is rare. No consensus has been reached for a clear definition and categorization. In the current study, we describe a cutaneous neoplasm; a squamomelanocytic tumor (SMT) with histological features combining those of a squamous cell carcinoma (SCC) and a malignant melanoma (MM). This is the second report of an oculocutaneous SMT, and concerns a subject with a 20-year history of solar lentigo coexisting with solar keratosis in the primary lesion. This type of tumor is quite rare, with a distinct cytological architecture and immunohistochemical features, and the differential diagnosis of SMT may be considered. However, the histogenesis, biological behavior and malignant potential of SMTs remain a matter of speculation. With regard to the treatment, complete surgical resection and close follow-up are recommended.

Melanocytic matricoma with melanocytic atypia: report of a unique case and review of the literature

Melanocytic matricoma is a rare cutaneous neoplasm of presumed anagen hair follicle origin with approximately 10 reported cases in the literature. Melanocytic matricomas are clinically and histopathologically distinct cutaneous nodular proliferations of matrical and supramatrical cells admixed with dendritic melanocytes, which typically occur in the sun-exposed areas of elderly patients. We report a new case with additional histopathologic features not previously described. An 82-year-old white man presented with an exophytic papule of the ear clinically suspicious for basal cell carcinoma. Histopathologic examination demonstrated a polypoid neoplasm consisting of an admixture of matrical and shadow cells with numerous interspersed dendritic and epithelioid melanocytes arranged singly and in large expansile nests. An unusual feature in this case included prominent melanocytic proliferation with associated nuclear atypia and increased mitotic activity. Although atypical and malignant melanocytic colonization has been reported in basal cell carcinomas and squamoproliferative lesions, to our knowledge, it has not been previously described in melanocytic matricomas. The biologic significance of atypical melanocytic proliferations within melanocytic matricomas is uncertain and requires further study of additional cases and long-term follow-up.

A rare case of a cutaneous squamomelanocytic tumor: revisiting the histogenesis of combined neoplasms

We describe what we believe to be the seventh report of a combined tumor with histologic features of both malignant melanoma and a squamous cell carcinoma, a squamomelanocytic tumor. An 82-year-old woman presented with a nondescript, skin-colored, firm papule on her nose. Histology showed 2 different neoplastic cell proliferations: atypical squamoid cells and irregularly shaped nests of atypical pigmented epithelioid cells (melanocytes) arranged in small to large nests at the dermal-epidermal junction and within the epidermis. Both components were closely admixed and restricted to the epidermis. Immunohistochemistry showed diffuse cytoplasmic reactivity for pancytokeratin in all areas supporting the histopathologic features of a squamous cell carcinoma. S-100 and melanoma antigen recognized by T cells 1 did not stain these areas and showed strong selective positivity for the atypical melanocytic component. A true malignant proliferation of 2 distinct cell phenotypes due to close paracrine interactions is our favored interpretation because of the intimate admixture, distinct immunohistochemical pattern, and unique histologic features. Perhaps, chronic sun damage (facial location and advanced age) and reduced immunity (history of other malignancies, particularly recent history of a basal cell carcinoma) played a complementary role for the development of the squamomelanocytic tumor.

Dermal squamomelano-cytic tumor: neoplasm of uncertain biological potential

We report a case of exceedingly rare cutaneous neoplasm with histological features of malignancy and uncertain biological potential. The nodular, darkly pigmented facial tumor with central exulceration, size 12 x 10 x 7 mm, of the skin 61-year-old man preauricular left was completely exised. Histologically tumor consists of atypical squamous cells, which express signs of moderate to significant pleomorphism, mitotically active, with foci forming of parakeratotic horn cysts ("pearls"). Characteristically tumor also consists of large number of atypical melanocytes with multifocal pattern, inserted between atypical squamous cells, and which contain large amount of dark brown pigment melanin. Immunohistochemically, squamous cells stain positively with keratin (CK116), melanocytes were stained with S -100 protein, HMB 45, and vimentin, but failed to stain with CK 116. To our knowledge this is the sixth reported case in world literature. The follow-up time of four years no evidence of recurrence or metastasis, similar all reported cases, but it is too short period in estimation to guarantee a benign course. However, it appears that this group of neoplasm may have different prognosis from pure squamous carcinoma or malignant melanoma.

Pigmented Squamous Cell Carcinoma

Although dendritic, melanin-containing melanocytes can be seen in a variety of epithelial neoplasms, only 0.01% to 7% of all squamous cell carcinomas (SCC) are pigmented. Furthermore, most reported cases have occurred in the oral and ocular mucosa, with relatively few cases reported to originate in the skin. Herein we report a case of a 61-year-old Caucasian male who presented with a large blue-black nodule on his left cheek, clinically suspicious for a melanoma; however, histological evaluation revealed an acantholytic pigmented squamous cell carcinoma. Previous cases are reviewed and the clinical and histological differential diagnoses are discussed.

Divergent differentiation in malignant melanomas: a review

The aim of this review was to document and discuss diagnostic problems associated with divergent differentiation ('metaplastic change') in malignant melanomas, defined as the development in these tumours of morphologically, immunohistochemically and/or ultrastructurally recognizable non-melanocytic cell or tissue components. Types of divergent differentiation reported in malignant melanoma include: fibroblastic/myofibroblastic, Schwannian and perineurial, smooth muscle, rhabdomyosarcomatous, osteocartilaginous, ganglionic and ganglioneuroblastic, neuroendocrine and probable epithelial. Divergent differentiation is certainly a rare phenomenon and, when it occurs, can be missed by unwary pathologists and lead to diagnostic uncertainty. A carefully chosen immunohistochemical panel and the input of electron microscopy can help to clarify the nature of the cellular differentiation of these tumours and lead to a correct final diagnosis. The clinical significance of such aberrations is uncertain, nor are the underlying mechanisms as yet well defined.

Malignant melanoma in the 21st century, part 1: epidemiology, risk factors, screening, prevention, and diagnosis

Malignant melanoma is an aggressive, therapy-resistant malignancy of melanocytes. The incidence of melanoma has been steadily increasing worldwide, resulting in an increasing public health problem. Exposure to solar UV radiation, fair skin, dysplastic nevi syndrome, and a family history of melanoma are major risk factors for melanoma development. The interactions between genetic and environmental risk factors that promote melanomagenesis are currently the subject of ongoing research. Avoidance of UV radiation and surveillance of high-risk patients have the potential to reduce the population burden of melanoma. Biopsies of the primary tumor and sampling of draining lymph nodes are required for optimal diagnosis and staging. Several clinically relevant pathologic subtypes have been identified and need to be recognized. Therapy for early disease is predominantly surgical, with a minor benefit noted with the use of adjuvant therapy. Management of systemic melanoma is a challenge because of a paucity of active treatment modalities. In the first part of this 2-part review, we discuss epidemiology, risk factors, screening, prevention, and diagnosis of malignant melanoma. Part 2 (which will appear in the April 2007 issue) will review melanoma staging, prognosis, and treatment.

Cutaneous squamous cell carcinoma: a comprehensive clinicopathologic classification

Cutaneous squamous cell carcinoma (SCC) includes many subtypes with widely varying clinical behaviors, ranging from indolent to aggressive tumors with significant metastatic potential. However, the tendency for pathologists and clinicians alike is to refer to all squamoid neoplasms as generic SCC. No definitive, comprehensive clinicopathological system dividing cutaneous SCCs into categories based upon their aggressiveness has yet been promulgated. Therefore, we have proposed the following based upon the malignant potential of SCC variants, separating them into categories of low (< or = 2% metastatic rate), intermediate (3-10%), high (greater than 10%), and indeterminate behavior. Low-risk SCCs include SCC arising in actinic keratosis, HPV-associated SCC, tricholemmal carcinoma, and spindle cell SCC (unassociated with radiation). Intermediate-risk SCCs include adenoid (acantholytic) SCC, intraepidermal epithelioma with invasion, and lymphoepithelioma-like carcinoma of the skin. High-risk subtypes include de novo SCC, SCC arising in association with predisposing factors (radiation, burn scars, and immunosuppression), invasive Bowen's disease, adenosquamous carcinoma, and malignant proliferating pilar tumors. The indeterminate category includes signet ring cell SCC, follicular SCC, papillary SCC, SCC arising in adnexal cysts, squamoid eccrine ductal carcinoma, and clear-cell SCC. Subclassification of SCC into these risk-based categories, along with enumeration of other factors including tumor size, differentiation, depth of invasion, and perineural invasion will provide prognostically relevant information and facilitate the most optimal treatment for patients.

Cutaneous squamous cell carcinoma: a comprehensive clinicopathologic classification. Part one

Cutaneous squamous cell carcinoma (SCC) includes many subtypes with widely varying clinical behaviors, ranging from indolent to aggressive tumors with significant metastatic potential. However, the tendency for pathologists and clinicians alike is to refer to all squamoid neoplasms as generic SCC. No definitive, comprehensive clinicopathological system dividing cutaneous SCCs into categories based upon their aggressiveness has yet been promulgated. Therefore, we have proposed the following based upon the malignant potential of SCC variants, separating them into categories of low (< or = 2% metastatic rate), intermediate (3-10%), high (greater than 10%), and indeterminate behavior. Low-risk SCCs include SCC arising in actinic keratosis, HPV-associated SCC, tricholemmal carcinoma, and spindle cell SCC (unassociated with radiation). Intermediate-risk SCCs include adenoid (acantholytic) SCC, intraepidermal epithelioma with invasion, and lymphoepithelioma-like carcinoma of the skin. High-risk subtypes include de novo SCC, SCC arising in association with predisposing factors (radiation, burn scars, and immunosuppression), invasive Bowen's disease, adenosquamous carcinoma, and malignant proliferating pilar tumors. The indeterminate category includes signet ring cell SCC, follicular SCC, papillary SCC, SCC arising in adnexal cysts, squamoid eccrine ductal carcinoma, and clear-cell SCC. Subclassification of SCC into these risk-based categories, along with enumeration of other factors including tumor size, differentiation, depth of invasion, and perineural invasion will provide prognostically relevant information and facilitate the most optimal treatment for patients.

Malignant Melanoma Metastatic to a Basal Cell Carcinoma Simulating the Pattern of a Basomelanocytic Tumor

We report a case of metastatic melanoma colliding with and colonizing a basal cell carcinoma (BCC) on the head of a 69-year-old man. The man had a prior history of multiple primary BCCs and melanomas. One of his primary melanomas, on the left scalp, recurred locally and resulted in the development of numerous in-transit metastases. A bluish nodule was noted on the postauricular area with clinical features consistent with a pigmented BCC. Dermoscopy showed some large gray-blue ovoid structures and blood vessels, features also consistent with BCC. However, the histologic features revealed that the nodule consisted of both metastatic melanoma as well as BCC. Melanoma was present adjacent to as well as within the epithelium of the BCC. The intimate association of melanoma cells within the nodules of BCC simulated the pattern of so-called "malignant basomelanocytic tumor," a recently proposed novel entity. To our knowledge, this is the first description of metastatic melanoma colonizing a BCC.

Combined High-Grade Basal Cell Carcinoma and Malignant Melanoma of the Skin (???Malignant Basomelanocytic Tumor???)

We describe two cases of a malignant cutaneous neoplasm with combined phenotypical features of high-grade basal cell carcinoma and malignant melanoma. Some tumor cells showed a keratinocytic phenotype (cytokeratins, p63) and others a melanocytic phenotype (HMB-45, MART-1, Melan-A, S100-protein). We favor the hypothesis of a tumor with bidirectional keratinocytic and melanocytic differentiation, an exceptionally rare event.

Pigmented squamous cell carcinoma of the conjunctiva of a horse

Abstract A heavily pigmented tumor was removed from the lateral, perilimbal, bulbar conjunctiva of a bay Thoroughbred horse. Excision was incomplete and the base of the tumor was lasered on the assumption that the tumor was a melanoma. No other ophthalmic lesions were seen. Histology showed the mass to be a pigmented squamous cell carcinoma (SCC). The prognosis and recommended treatment protocols are different for SCC and melanoma. This is, to the best of our knowledge, the first report of an ocular, pigmented SCC in the veterinary literature.

Malignant Basomelanocytic Tumor Manifesting as Metastatic Melanoma

We report a case of an unusual basomelanocytic tumor from the scalp of a 56-year-old man. A 56-year-old white man presented with a scalp lesion that was biopsied and interpreted as a basal cell carcinoma. Fourteen months later, metastatic melanoma was discovered in a cervical lymph node and the liver. A subsequent biopsy from the area of the previously biopsied basal cell carcinoma of the scalp showed an invasive malignant melanoma. Immunohistochemical stains performed on the original scalp specimen showed biphasic immunohistochemical profile. A population of neoplastic cells was strongly positive for the melanocytic markers Melan-A, HMB-45, and tyrosinase and showed weak focal immunoreactivity for S-100. A second population of cells was strongly immunoreactive for keratin (wide-spectrum polyclonal antibody) and BerEp4. To our knowledge, this is the first description of a malignant basomelanocytic tumor complicated by metastatic melanoma.

Melanoma with Prominent Pigment Synthesis (Animal-Type Melanoma)

Melanoma with prominent pigment synthesis or animal-type melanoma (ATM) is a very rare type of melanoma. Its histogenesis has not been elucidated and ultrastructural features have not been described in human beings. We present an additional case of ATM in a 28-year-old woman with positive sentinel node biopsy and provide the results of electron microscopic studies. Histopathologically, the skin lesion was composed of heavily pigmented neoplastic cells mostly arranged as large sheets, focally also in a nodular growth pattern. After bleaching, the neoplastic cells demonstrated round nuclei with 1 or rarely 2 conspicuous nucleoli and a prominent nuclear membrane and abundant, gray, slate-like cytoplasm. Some cells demonstrated round cytoplasmic inclusions. There was no nuclear pleomorphism, and only a few mitotic figures could be found after extensive search. Multiple areas of necrosis en masse of tumor cells were seen. The lymph node biopsy revealed a complete effacement of the lymph node architecture by the extensive proliferation of hyperpigmented cells in the parenchyma. Immunohistochemically, the same pattern of staining was seen on the bleached and unbleached slides both in the skin and in the lymph node. The neoplastic cells stained positively with MiTF (nuclei), NSE, NKI/C3, tyrosinase (weak), p53, and CD68. S-100 protein, HMB45, Melan A, Mac367, and lysozyme reacted negatively. Occasional cells (<1%) reacted with MIB-1. Ultra-structural studies revealed that the neoplastic cells possessed a large, indented nucleus with a prominent nuclear membrane, a single (para) centrally located nucleolus, and peripherally marginated chromatin. The cytoplasm was abundant and contained numerous single melanosomes and rare compound melanosomes. The melanosomes were in stages II to IV of maturation, with a marked predominance of stage II and stage III melanosomes. There was a high number of aberrant melanosomes with a wide variety of configurations. Melanophages were a minor component of the lesion. Our ultrastructural studies provide unequivocal evidence that ATM is a neoplasm of melanosome-producing cells. We also review the literature on ATM.

Pigmented squamous cell carcinoma of the uterine cervix

A 57-year-old female presented with an abnormal Pap smear. Colposcopic examination of the cervix revealed white mucosa with erosion and several areas of black pigmentation. After a colposcopically directed biopsy and loop conization, radical hysterectomy and bilateral salpingo-oophorectomy with pelvic and paraaortic lymphadenectomy were performed. Pathological examination disclosed an invasive squamous cell carcinoma admixed with many dendritic melanocytes. Melanin granules were present within the melanocytes and tumor cells. Although similar tumors have been reported in other sites, this is the first report to our knowledge of a pigmented squamous cell carcinoma of the uterine cervix.

Follicular baso-squamous melanocytic tumour of the skin

AIMS

We describe a previously unrecognized pigmented tumour of the skin and suggest a possible relationship with the follicular bulb.

METHODS AND RESULTS

A pigmented epithelial neoplasm clinically simulating a malignant melanoma of the skin was present in a 92-year-old woman, on her left leg. It was composed of three cell types: squamous cells with trichilemmal keratinization, basaloid cells and dendritic melanocytes. The presence of three cell types was confirmed by immunohistochemistry and electron microscopy.

CONCLUSIONS

The tumour showed differentiation towards the hair follicular bulb and the descriptive term of follicular baso-squamous melanocytic tumour is suggested.

A study of eleven cutaneous malignant melanomas in adults with small-cell morphology: emphasis on diagnostic difficulties and unusual features

AIMS

To describe the clinicopathological and immunohistochemical features of cutaneous malignant melanomas with a pure or mixed small-cell pattern in 11 adult patients, and to discuss the diagnostic difficulties encountered.

METHODS AND RESULTS

Haematoxylin and eosin-stained sections of each case of cutaneous small-cell malignant melanoma, together with locally recurrent skin lesions and, where available, metastatic deposits, were re-examined. Available immunohistochemical sections were evaluated. Clinical follow-up data were obtained in each case. One patient presented with metastatic disease, the others presented with cutaneous lesions. Suggested initial diagnoses included malignant melanoma, non-Hodgkin's lymphoma, Merkel cell carcinoma and sarcoma. All the tumours were in the vertical growth phase. Nine had a junctional component, often inconspicuous. The lesions showed either a pure small-cell pattern or a mixed pattern with more conventional areas. In one case, there was colonization of a basal cell carcinoma by invasive malignant melanoma. Variable retention of small-cell morphology in local recurrences and metastases was observed, although in some cases more typically pleomorphic cells were present. In the cases tested, there was strong immunostaining for S100 protein and NKI-C3, and variable immunostaining for HMB45 and Melan-A. Non-melanocytic markers were negative.

CONCLUSIONS

The possibility of a small-cell malignant melanoma should be considered in the assessment of cutaneous and non-cutaneous small-cell neoplasms. The correct diagnosis requires careful evaluation for junctional activity, melanin production and the use of a panel of melanocytic markers.