Melanocytic matricoma: a report of two cases of a new entity

Atypical Melanocytic Matricoma: A Case Report with Molecular Studies

ABSTRACT

Melanocytic matricoma is a rare benign pilar tumor characterized by matrical differentiation and interspersed dendritic melanocytes. It may show cellular atypia and brisk mitotic activity. Histological characterization of some lesions may be difficult. In addition, because the reported cases are few and have limited follow-up, there is insufficient experience to define outcome-based criteria for malignancy. Some cases of melanocytic matricoma with more prominent atypia have been reported as malignant, but their clinical behavior is uncertain. We present a melanocytic matricoma with interspersed benign dendritic melanocytes, but moderate basaloid atypia, focally brisk mitotic activity, and atypical mitoses. Despite the apparently good delimitation of this tumor, higher magnification revealed a slightly irregular border. However, overt malignant features such as necrosis, frank asymmetry, deep infiltration, and ulceration were not present. This tumor showed a complex aberrant genomic profile with multiple whole chromosomes or chromosomal arms, losses, and duplications. The tumor mutational burden was high. A loss-of-function alteration in CDKN2A and a loss-of-function mutation in TP53 were also present. This unexpected molecular profile contrasts with the relatively bland histology of the tumor and is in line with the difficulties in microscopic differential diagnosis between melanocytic matricoma and an indolent malignant pilomatrical tumor. We suggest that molecular studies and longer follow-up periods may help to further understand and more precisely categorize borderline pilomatrical tumors with melanocytic hyperplasia.

Melanocytic Matricoma With Atypical Histopathological Features: A Case Report of an Extremely Rare Entity and Review of the Literature

ABSTRACT

Melanocytic matricoma with atypical features is a rare, biphasic adnexal neoplasm displaying hair matrix differentiation, with only 3 reported cases worldwide. Generally, the lesion comprised a solid matrical and supramatrical cell proliferation, admixed with intermediate cell aggregates with sparse anucleated "shadow cells" and a prominent pigmented melanocytic hyperplasia. We report the case of a 78-year-old man with a slow-growing crusted lesion on the frontal left scalp, which in a matter of 1-2 months became a 0.6 cm well-defined, black purplish exophytic nodule. Histopathologically, the lesion presented a well-circumscribed border with a nodular dermal growth pattern, presenting different architectural features varying from benign pilomatricoma-like changes to atypical features such as moderate-to-high nuclear pleomorphism in both basaloid (matrical/supramatrical) and epidermal (keratinous) components. Strong nuclear and cytoplasmic positivity for β-catenin was observed in matrical cells, whereas prominent cytoplasmic membrane positivity for Melan-A in dendritic melanocytes. Owing to the evidence of atypical cytological features, we propose the "atypical/borderline" category of melanocytic matricoma as part of a possible spectrum among matrical neoplasms. Pathologists should be aware of any atypical histopathological features while reporting cases due to their potential malignant transformation.

Melanocytic Matricoma: A Potential Mimic of Malignant Melanoma

Melanocytic matricoma is a rare dermal tumor that typically presents on the sun-damaged skin of older patients. While there is controversy in the literature regarding the proper characterization of this tumor, there are certain histological and immunohistochemical features that have been described. This report presents a case of melanocytic matricoma with several unusual features that were initially feared to be malignant melanoma. Careful histologic and immunohistochemical analysis was required to rule out malignant melanoma and make the correct diagnosis. Given the rarity of melanocytic matricoma and the potential for it to mimic malignant melanoma, it is important for pathologists to keep melanocytic matricoma on the differential and be aware of the clinical, histological, and immunohistochemical features of this tumor.

Metastatic melanoma and rare melanoma variants: a review

The histopathological diagnosis of melanoma is fraught with potential pitfalls. In the setting of cutaneous metastatic melanoma, it is important to recognise the various histological patterns that can be encountered from the more common to the rare, including epidermotropic, folliculotropic, naevoid, and blue naevus-like. In addition, melanoma is notorious for phenotypic plasticity. Thus, there are many different subtypes and cytomorphological variations that can be difficult to recognise as melanoma, particularly in the recurrent or metastatic setting. Select melanoma variants including primary dermal, clear cell, plasmacytoid, signet ring cell, small cell, myxoid, rhabdoid, and dedifferentiated melanoma will be discussed, in addition to composite melanocytic neoplasms. This review is intended to remind the practitioner of key concepts of metastatic disease and select rare melanoma variants, while providing practical guidelines for accurate diagnosis.

Malignant Melanocytic Matricoma: A Rare Skin Tumor That Can Clinically Mimic Melanoma

Malignant melanocytic matricoma (MMM) is an extremely rare skin malignant neoplasm composed of epithelial cells with matrical differentiation and dendritic melanocytes. We found only 11 cases reported in the literature to date according to the databases consulted (PubMed/Medline, Scopus, and Web of Science). Here, we report a case of MMM in an 86-year-old woman. A histological examination showed a dermal tumor with a deep infiltrative pattern, without an epidermal connection. On immunohistochemical staining, tumor cells were positive for cytokeratin AE1/AE3, p63, and beta-catenin (nuclear and cytoplasmic staining) and negative for HMB45, Melan-A, S-100 protein, and androgen receptor. Melanic antibodies highlighted scattered dendritic melanocytes in tumor sheets. The findings did not support the diagnosis of melanoma, poorly differentiated sebaceous carcinoma, and basal cell carcinoma, but supported the diagnosis of MMM.

Melanocytic matricoma with atypical features: A case of malignant melanocytic matricoma?

Melanocytic matricoma is a rarely reported, benign cutaneous adnexal neoplasm composed of epithelial cells exhibiting differentiation towards hair matrix as well as admixed, pigmented, dendritic melanocytes. The proposed malignant counterpart to melanocytic matricoma, malignant melanocytic matricoma (MMM), is even more rare. Here we report a case of a melanocytic matricoma with atypical features in a 92-year-old female with a 1.2-cm pigmented nodule on the right nasal sidewall. Histopathology revealed a well-circumscribed dermal tumor composed of atypical matrical cells with scattered aggregates of anucleate keratinocytes (ghost cells), prominent intratumoral pigment, numerous mitotic figures (88 mitosis/10 high-power field [HPF]), and intermixed dendritic melanocytes. A literature review was performed for MMM to determine if the current case fit diagnostic criteria for this entity. Including the current case, 12 cases of MMM were identified and analyzed to investigate common clinical and histopathologic features. MMM commonly occurred on the head and neck (7/12 cases) of older individuals (median age of 80) with a slight male predominance (male-to-female ratio of 3:1) and on histopathology presented as a multinodular dermal tumor composed of mitotically active (average mitotic rate of >50 mitoses/10 HPF) pleomorphic epithelial cells with foci of ghost cells. Dendritic melanocytes were found throughout the tumor lobules in all cases. Given that only two of 12 cases have exhibited locally aggressive behavior, further study is warranted to determine the true malignant potential of MMM.

Melanocytic Panfolliculoma: A Case Report of a Rare Benign Follicular Tumor

ABSTRACT

Panfolliculomas (PF) are rare, benign, follicular tumors that differentiate toward multiple components of the hair follicle, and several variants have been described. We present a case of a rare pigmented PF presenting on actinically damaged skin in an 83-year-old man, which was clinically concerning for malignancy. This tumor arose near an area of atypical squamous proliferation and has evidence of infundibular, outer root sheath, and matrical differentiation and foci of heavy melanin pigmentation and increased melanocytes. We propose the novel designation of "melanocytic PF," akin to melanocytic matricoma but with panfollicular differentiation.

Melanocytic matricoma: A report of three cases, review of the literature and suggestion of a new terminology

Melanocytic matricoma is a rare, biphasic adnexal tumor. It typical presents as a pigmented papule on the sun-damaged skin of elderly patients. Histopathology shows a dermal nodule composed of basaloid cells, ghost cells and deeply pigmented dendritic melanocytes. The basaloid cells are usually positive for β-catenin and these tumors show overlapping histopathological and molecular features with pilomatricoma. Here we review the literature on melanocytic matricoma and present three new cases. We suggest different terminology to reflect the overlapping features with pilomatricoma, that recognizes that melanocytic matricoma is likely to be a variant of pilomatricoma associated with melanocytic hyperplasia. Although melanocytic matricoma is usually considered benign, malignant transformation has been reported. This highlights the need for increased awareness of this entity. This article is protected by copyright. All rights reserved.

Ki67/MART1 and p63/SOX10 Dual Immunohistochemistry Allows a Correct Interpretation of the Melanocytic Component in the Diagnosis of Pigmented Pilomatricoma

Pilomatricoma is a relatively common benign cutaneous adnexal tumor and a well-recognized entity, while its pigmented variant is far less common and less reported. Its estimated frequency ranges from 11 to 24%, according to a limited number of published case series. This article describes the case of a 42-year-old man presenting a firm subcutaneous nodule of the periareolar region. Histopathologic examination revealed a cystic lesion composed of matrical and supramatrical cells accompanied by a foreign body granulomatous cell reaction. Interestingly, a hyperpigmented area with numerous hyperplastic melanocytes and few mitoses was detectable. In order to assess the cell lineage of the mitotically active component in the hyperpigmented area, double immunohistochemistry with Ki67/Mart1 and p63/SOX10 was performed. Pigmented pilomatricoma is an underrecognized, underreported variant, and double immunohistochemistry stain is an effective tool in providing the correct interpretation of the proliferative activity in the different cellular populations.

Current Diagnosis and Treatment Options for Cutaneous Adnexal Neoplasms with Follicular Differentiation

Neoplasms derived from follicular tissue are extremely rare. Clinically, they are reported as non-symptomatic, slow-growing nodules. These lesions are mainly benign, but the malignant type can occur. Mainly middle-aged people (50-60 years of age) are affected. These carcinomas are mainly localized on the head and neck or torso. They can be locally aggressive and infiltrate surrounding tissue and metastasize to regional lymph nodes. In the minority of cases, distant metastases are diagnosed. Quick and relevant diagnosis is the basis of a treatment for all types of tumors. The patient's life expectancy depends on multiple prognostic factors, including the primary tumor size and its mitotic count. Patients should be referred to a specialized skin cancer center to receive optimal multidisciplinary treatment. This article tries to summarize all the information that is currently available about pathogenesis, diagnosis, and treatment methods of follicular tumors.

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.

Melanocytic Matricoma With Consumption of the Epidermis: An Atypical Histologic Attribute or a Malignant Variant?

Melanocytic matricoma is a recently described cutaneous adnexal tumor composed of matrical and supramatrical cells admixed with pigmented dendritic melanocytes, thought to recapitulate the anagen bulb of the hair follicle. We report a case of a 75-year-old white man, which demonstrates consumption of the epidermis that is defined as thinning of the epidermis with attenuation of the basal and suprabasal layers and loss of the normal rete architecture in areas of direct contact with neoplastic cells. It has been associated with aggressive histologic features in melanoma and likely represents an early phase of ulceration due to attenuation. Epidermal consumption has not been previously reported in nonmelanocytic tumors and it is uncertain whether this atypical histologic feature represents a sign of malignant behavior in this rare tumor.

Malignant Melanocytic Matricoma: A Report of 2 Cases and Review of the Literature

BACKGROUND

To describe 2 cases of melanocytic matricoma with malignant histological features and systematically review previously reported cases of malignant melanocytic matricoma.

METHODS

Two cases of malignant melanocytic matricoma were identified from the practice of the authors. Additional 3 cases were identified in the literature. The clinical and pathological features of these 5 cases are described.

RESULTS

Malignant melanocytic matricoma occurs predominantly in sun-damaged skin of elderly individuals. The tumor is composed of atypical epithelial cells with brisk mitotic activity showing evidence of matrical keratinization and widespread positivity with beta-catenin. There is an admixed cytologically bland dendritic melanocytic component. To date, local recurrence has occurred in one case, but no cases of disseminated disease or death have been reported.

CONCLUSIONS

Recognition of this rare tumor and separation from a range of diagnostic mimics is important to ensure adequate treatment by local excision and to allow further cases to be identified to better define the biological potential of this lesion.

[Skin adnexal tumors with follicular differentiation]

Skin adnexal tumors with predominantly follicular differentiation represent a clinicopathological heterogeneous group of neoplasms and are classified according to the cytologically achieved differentiation of the follicular compartment. Given the complex structure of non-neoplastic hair follicles it is not surprising to find varying differentiations in neoplasms and there are overlapping clinicopathological features between the established entities. The use of immunohistochemical staining has only a limited value in the diagnosis of follicular neoplasms.

Skin tumors with matrical differentiation: lessons from hair keratins, beta-catenin and PHLDA-1 expression

BACKGROUND

Pilomatricomas are tumors that emulate the differentiation of matrix cells of the hair follicle, showing cortical differentiation, with sequential expression of K35 and K31 keratins. Beta-catenin gene is frequently mutated in pilomatricoma, leading to beta-catenin nuclear accumulation, and to downstream expression of LEF1. Skin matrical tumors other than pilomatricoma are very rare, and comprise purely matrical tumors and focally matrical tumors. We aimed at studying cortical differentiation, beta-catenin pathway and expression of the follicular stem-cell marker PHLDA1 in a series of matrical tumors other than pilomatricoma.

METHODS

In 36 prospectively collected tumors, K31, K35, CK17, LEF1, HOXC13, beta-catenin and PHLDA1 expressions were evaluated. Five pilomatricomas were used as controls.

RESULTS

In 18 purely matrical tumors (11 matrical carcinomas, 4 melanocytic matricomas, 3 matricomas) and 18 focally matrical tumors (11 basal cell carcinomas, 3 trichoepithelioma/trichoblastomas, 4 others), sequential K35, HOXC13 and K31 expressions were found, indicating cortical differentiation. Germinative matrix cells were always CK17-, and showed nuclear beta-catenin accumulation, with LEF1 and PHLDA1 expressions.

CONCLUSIONS

Nuclear beta-catenin and LEF1 expression was highly conserved in matrical tumors, and suggested a common tumorigenesis driven by Wnt pathway activation. PHLDA1 was consistently expressed in matrical tumors and in areas of matrical differentiation.

Agminated pigmented matricoma: a case of a unique tumor with a multifocal appearance composed of neoplastic matrical cells with a significant component of melanocyte

Matricoma is benign follicular neoplasm with the same constituent cells as pilomatricoma but with a different silhouette. Matricoma consists mostly of solid aggregations of matrical cells, as opposed to pilomatricoma, which is often a cystic lesion. We herein describe a case of agminated pigmented matricoma. A 27-year-old Japanese man visited our hospital complaining of three separate, pigmented, firm and sessile nodules on the back. Histopathologic examination revealed mostly solid aggregations of matrical and supramatrical cells located mainly within the dermis and the upper part of the subcutis. Shadow cells were present mostly within the aggregations. At higher magnifications, occasional indication of inner sheath differentiation, in addition to differentiation toward hair in the form of shadow cells, could be discerned in the center of the aggregations. The matrical and supramatrical cells within the aggregations were relatively uniform in size and shape, and contained several mitotic figures. Heavily pigmented melanocytes were present within the aggregations of matrical and supramatrical cells, and heavily pigmented melanophages were found in adjacent stroma. Pigmentation is a rare event in benign and malignant adnexal tumors, and to our knowledge, no similar case has been reported.

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.

Pilomatrix carcinoma of the clitoris

Pilomatrix carcinoma, a malignant counterpart of pilomatrixoma, is a rare skin neoplasm composed of basaloid and shadow cells that characterize differentiation toward the hair matrix. The authors present a case of pilomatrix carcinoma of the clitoris, a very unusual location not previously reported. Diagnostic criteria and differential diagnoses are discussed. Pilomatrix carcinoma should be differentiated from benign pilomatrixoma and other carcinomas with shadow cells, including basal cell carcinoma with matrical differentiation and metastases of visceral carcinomas with shadow cells.

An unusual composite pilomatrix carcinoma with intralesional melanocytes: differential diagnosis, immunohistochemical evaluation, and review of the literature

We report a case of an extremely rare histologic combination of pilomatrix or pilomatrical carcinoma with admixed melanocytes within the same tumor mass. Pilomatrix carcinoma is a neoplasm of low-grade malignancy that is characterized by a tendency for recurrence but low risk of metastasis. A 77-year-old male presented with a nodule on the bridge of the nose that was excised. Histologically, it was typified by asymmetry and poor circumscription, the presence of several variably sized and shaped basaloid aggregations, and surface ulceration. The tumors were composed of pleomorphic basaloid cells with prominent nucleoli and frequent mitoses (some of which were atypical) accompanied by central areas with keratotic material, shadow cells, and foci of necrosis. In addition, intermingled with the pilomatrix carcinoma, several easily identified pigmented cells with dendritic processes were present singly and as small aggregates. There was no atypia associated with the melanocytic component. Immunohistochemistry revealed the CK14 to be positive mainly within the keratinizing and the squamous epithelial elements of the tumor. The melanocytic component was strongly immunoreactive for S100, melanoma cocktail (HMB45 and Melan-A), and microphthalmia transcription factor. Pilomatrix carcinoma with melanocytes should be distinguished from the conventional pilomatrixoma with pigmentation, melanocytic matricoma, melanoma, and pigmented basal cell carcinoma with matrical differentiation. Clinicians and pathologists should be aware of the occurrence of pilomatrix carcinoma with melanocytes because of its potential for diagnosis as melanoma. This peculiar lesion recapitulates the intimate relationship existing between matrical epithelium and melanocytes in the embryonal hair follicle or in the anagen stage of the hair cycle. It is possible that sun damage played a role in stimulating migration of melanocytes among matrical cells in this case.

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.

Unusual occurrence of a melanoma with intermixed epithelial component: a true melanocarcinoma?: case report and review of epithelial differentiation in melanoma by light microscopy and immunohistochemistry

We report a case of a 27-year-old woman with a nonpigmented lesion on the right scalp. Histological examination showed a malignant nodular neoplasm with 2 distinct but intimately admixed components: a malignant melanoma with a spindle component and an unusual glandular component. Immunohistochemical studies demonstrated epithelial differentiation on the basis of cytokeratin (CAM5.2 and AE1/AE3) expression in the glandular component and melanocytic differentiation (HMB-45, PNL2, MITF, and S-100) of the spindle cell component. A single melanocytic marker (MITF) was expressed in both components, raising the possibility of dual differentiation in a single tumor, rather than the alternative considerations of a collision tumor or a reactive pseudoepitheliomatous hyperplasia with eccrine duct lumen formation within a melanoma. This unusual tumor with both melanocytic and epithelial components may represent a true melanocarcinoma, which becomes a plausible consideration, in view of melanoma plasticity and recent experimental evidence and speculation about the role of stem cells in melanoma.

Cell adhesion protein expression in melanocytic matricoma

Melanocytic matricoma is a rare neoplasm thought to recapitulate the hair follicle in anagen. The tumor forms a nodule in the dermis containing basaloid, intermediate and shadow cells admixed with pigmented melanocytes dispersed as single dendritic cells. Because cadherins and catenins are crucial in the development of hair tumors, we examined the expression of E(epithelial)-, P(placental)-, N(nerve)-cadherin and beta-catenin in a melanocytic matricoma. A 66-year-old Caucasian woman with a history of breast cancer presented with a pigmented nodule on the shoulder. Pathology revealed a melanocytic matricoma with S-100 and HMB45-positive melanocytes. E- and P-cadherin were localized at the cell membrane of basaloid and differentiating keratinocytes, and in melanocytes, recapitulating the anagen hair. Both cadherins were absent in shadow cells. N-cadherin was not expressed. Beta-catenin had a differential distribution, in the nucleus and cytoplasm of basaloid cells, but at the cell membrane in differentiating cells and negative in shadow cells, paralleling the expression of E- and P-cadherin. Our results support the previously hypothesized resemblance of the tumor to the hair bulb in anagen and suggest a transcriptional role of beta-catenin in the development of this rare neoplasm.

Melanocytic matricoma in a dog

We report a tumor that developed at the root of the tail in a male, 2-year-old Shih Tzu dog. Histologically, the tumor consisted of basaloid epithelial cells, with shadow cells and neoplastic melanocyte proliferation. Immunohistochemically, epithelial components were positive for keratin/cytokeratin but basaloid cells were negative. Mononuclear or multinuclear melanocytes were positive for vimentin, S-100 protein, and HMB-45. In conclusion, this dog was diagnosed with canine melanocytic matricoma on the basis of the similarity of the histologic and immunohistochemical features in humans, and it may be the first case in an animal.