Basaloid neoplasms in nevus sebaceus

Rate of Benign and Malignant Secondary Tumors Associated With Nevus Sebaceous: A Systematic Review and Meta-Analysis

BACKGROUND

Nevus sebaceous (NS) is a rare congenital skin lesion affecting approximately 0.3% of all newborns. Although benign, NS lesions can harbor malignant secondary tumors. The published rate of development of these malignant tumors varies. This meta-analysis aimed to identify the rate of malignant and benign secondary neoplasms occurring in NS.

METHODS

A literature search was conducted using PubMed, Embase, and Web of Science from inception to April 2023. Eligible studies reported incidence or risk of secondary neoplasms in patients with NS. Two independent reviewers screened studies, extracted data, and assessed the quality of included studies. The primary outcome was the pooled incidence of secondary neoplasms. Studies with sample sizes greater than 50 patients were eligible for meta-analysis using the random-effects model.

RESULTS

Twenty-eight studies were identified, 22 of which were eligible for meta-analysis. The overall rate of secondary neoplasms was 12.8% (95% confidence interval [Cl], 9.2%-17.6%). The rates of development of malignant and benign tumors were 2.4% (95% CI, 1.4%-4.1%) and 10.3% (95% CI, 7.5%-13.9%), respectively. The rate of development of basal cell carcinoma was 1.7% (95% CI, 0.9%-3.2%), whereas the rate of the development of syringocystadenoma papilliferum was 3.6% (95% CI, 2.5%-5.3%) and that if trichoblastoma was 2.6% (95% CI, 1.7%-3.8%).

CONCLUSIONS

Although the rate of development of malignant tumors within a primary NS lesion is low, it is not negligible. Prophylactic early excision remains a viable approach to prevent secondary malignant neoplasms, address cosmetic and functional complications, and preempt the need for complex reconstruction in the future. We propose that resection of NS lesions in childhood remains a reasonable first-line option in the appropriate patient keeping in mind that it may leave an undesirable scar.

Malignant Melanoma Arising in a Prolific Nevus Sebaceus With Colonization of Trichoblastoma

ABSTRACT

Nevus sebaceus (NS) is a cutaneous hamartoma typically found on the head and neck, with a prevalence of 0.3% in newborns. Most NS are quiescent; however, benign and malignant lesions have been reported to arise within these nevi. Malignant transformation is not common but mainly includes basal cell carcinoma and squamous cell carcinoma. Malignant melanoma arising in NS is exceedingly rare, with only 2 previously documented cases. In this article, we report the first case of malignant melanoma arising in a NS in a 68-year-old man in the United States.

Secondary neoplasms arising from nevus sebaceus: A retrospective study of 450 cases in Taiwan

Nevus sebaceus is frequently associated with the development of secondary neoplasms. Incidences of malignant transformation vary among different reports and few data is available regarding Asian populations. We aimed to determine the characteristics of secondary tumors developing from nevus sebaceus in a Taiwanese population and to review the published work. Patients with clinically and histologically confirmed nevus sebaceus were identified from 1992 to 2012 in a medical center. Among the 450 cases of nevus sebaceus, 38 secondary neoplasms were noted, accounting for 8.5% of all cases. Benign tumors represented more than 80% of all tumors. Syringocystadenoma papilliferum (2.7%) was the most common benign tumor, followed by trichoblastoma (1.6%) and trichilemmoma (1.6%) whereas basal cell carcinoma (0.9%) was the most frequent malignant tumor on nevus sebaceus and its clinical features were not typical. All the malignant tumors on nevus sebaceus were noted only in adulthood and the mean age of those with basal cell carcinoma was significantly older than that of trichoblastoma (P = 0.028). Our study concludes that malignant transformation is rare in nevus sebaceus and occurs uniquely in adulthood. On the basis of the findings, prophylactic excision of nevus sebaceus can be elective during childhood but is strongly advocated at puberty due to the increased risk of malignant transformation with time.

Secondary neoplasms associated with nevus sebaceus of Jadassohn: a study of 707 cases

BACKGROUND

Nevus sebaceus is commonly associated with the development of secondary neoplasms. Data on the frequency of malignant tumors vary considerably in published reports.

OBJECTIVE

We sought to analyze the distribution of secondary neoplasm in nevus sebaceus.

METHODS

A retrospective analysis of all cases of nevus sebaceus diagnosed at the Ackerman Academy of Dermatopathology from 1999 to 2012 was conducted.

RESULTS

A total of 706 patients (707 specimens) were included in the study. Trichoblastoma was the most frequent benign tumor (n = 52, 7.4%) followed by syringocystadenoma papilliferum (n = 33, 5.2%). Malignant tumors were present in 2.5% of the specimens with basal cell carcinoma being the most common (n = 8, 1.1%) followed by squamous cell carcinoma (n = 4, 0.57%). The incidence of secondary neoplasms was statistically related to age and anatomic site (P < .05). Almost all malignant tumors were seen in adults.

LIMITATION

Some of our cases were referred for second opinion and there may be a bias in our data toward unusual secondary neoplasms.

CONCLUSION

Our study confirms that most of the secondary neoplasms arising in association with nevus sebaceus are benign. As no malignant tumors were seen in children, we believe it is reasonable to delay surgical management until adolescence.

Hybrid follicular cyst (pilomatrical and infundibular) arising within a sebaceous nevus

A 7-year-old girl presented with a 3-month history of a small blue-brown papule arising within a large sebaceous nevus on her temporal scalp. A punch excision was performed that demonstrated a hybrid follicular cyst. The majority of the cyst wall displayed pilomatrical differentiation consisting of basaloid matrical-type cells with luminal shadow cell keratinization. The matrical epithelium displayed strong membranous, cytoplasmic, and nuclear staining for β-catenin. Only a small component of the wall displayed infundibular differentiation. These findings were consistent with a hybrid follicular cyst predominantly displaying pilomatrical differentiation with only a small component of infundibular lining. The most common tumors arising within sebaceous nevi are the syringocystadenoma papilliferum and trichoblastoma. Follicular cysts with infundibular (sebaceous cyst) and trichilemmal (pilar cyst) differentiation are exceedingly common, although their development within sebaceous nevi appears to be rare. We report a rare case of a hybrid follicular cyst with matrical differentiation occurring within a sebaceous nevus.

Nevus sebaceous revisited

Nevus sebaceous of Jadassohn is a hamartoma with a combination of abnormalities of the epidermis, hair follicles, and sebaceous and apocrine glands. Herein, we discuss the results of an extensive literature review on the topic of nevus sebaceous with a particular focus on the debate about the necessity for prophylactic excision. We also focus on the documentation of associated malignant tumors that were reported to develop within NS. In addition to reporting the number and types of neoplasms, we documented the recommendations of all authors for therapeutic handling of these nevi.

Multiple large pilomatricomas in the setting of diffuse epidermal nevi

Epidermal nevi are hamartomas arising from the embryonic ectoderm during early embryonic stages, resulting in cutaneous mosaicism. We describe a patient with diffuse epidermal nevi and multiple large pilomatricomas arising near or within epidermal nevi.

Mucoepidermoid (adenosquamous) carcinoma, trichoblastoma, trichilemmoma, sebaceous adenoma, tumor of follicular infundibulum and syringocystadenoma papilliferum arising within 2 persistent lesions of nevus sebaceous: report of a case

Nevus sebaceous of Jadassohn (SNJ) is a congenital, hamartoma of multiple skin structures and may classically evolve through several stages of maturation. Many neoplasms have been reported to arise in association with SNJ, most commonly trichoblastoma and syringocystadenoma papilliferum. The coexistence of 3 or more tumors arising simultaneously within 1 lesion of SNJ is very rare. We report a case of a 66-year-old woman with a coexistence of trichoblastoma, trichilemmoma, sebaceous adenoma, tumor of follicular infundibulum, syringocystadenoma papilliferum, and mucoepidermoid or adenosquamous carcinoma arising in 2 separate and persistent SNJ exhibiting on her face with subsequent parotid node metastasis. This report illustrates an extraordinary case of adnexal neoplasms displaying diverse lines of differentiation arising within lesions of SNJ. We also reported the second instance of mucoepidermoid arising within the lesion of SNJ and also added sebaceous adenoma to the list of sebaceous tumors arising within this lesion. Prophylactic excision or at least close clinical surveillance for sudden development of new growths is warranted.

Trichoblastomas with Merkel cell proliferation in nevi sebacei in Schimmelpenning-Feuerstein-Mims syndrome--histological differentiation between trichoblastomas and basal cell carcinomas

The hallmark of Schimmelpenning-Feuerstein-Mims syndrome (SFMS) is a systematized nevus sebaceous that follows Blaschko lines and usually involves the face. It represents a rare congenital nevus syndrome with alterations of skin, bones, CNS, eyes and heart. Nevi sebacei can proliferate and develop into epithelial tumors like trichoblastoma, syringocystadenoma and basal cell carcinoma. The histological differentiation between basal cell carcinoma and trichoblastoma is difficult. We present an adult woman with SFMS who was followed by multiple specialties since birth without the correct diagnosis being made. She was referred to us with the diagnosis of multiple basal cell carcinomas of head and face. Our diagnosis of systematized nevus sebaceus was crucial for the correct classification of SFMS. We identified multiple trichoblastomas in the nevi sebacei and could exclude basal cell carcinomas. The essential clue was the detection of multiple Merkel cells within the epidermal layer by cytokeratin 20 staining.

Epidermodysplasia verruciformis-associated and genital-mucosal high-risk human papillomavirus DNA are prevalent in nevus sebaceus of Jadassohn

BACKGROUND

The hamartoma nevus sebaceus (NS) presents at birth or early childhood as a yellowish plaque characterized histologically by variable acanthosis, papillomatosis, sebaceus hyperplasia, and proliferations of adnexal structures. Clinically apparent human papillomavirus (HPV) infection is also recognized by acanthosis and papillomatosis.

OBJECTIVE

We sought to determine the prevalence and physical state of HPV DNA in NS.

METHODS

DNA was retrieved from 44 formalin-fixed, paraffin-embedded samples of NS (22 with secondary tumors [eg, trichoblastoma, verruca, syringocystadenoma papilliferum] and two epidermal nevi [EN]). Nested polymerase chain reaction with multiple degenerate consensus and type-specific primers and direct sequencing of polymerase chain reaction products was performed. For selected cases, in situ hybridization using probes specific for HPV 5 and 8 and for high-risk genital-mucosal HPV types was performed.

RESULTS

HPV DNA was detected in 82% of NS and both EN, and consisted of genital-mucosal HPV types in 52% (HPV 6, 16, and 33) and a diverse variety of epidermodysplasia verruciformis-associated HPV types in 61%, including well-known epidermodysplasia verruciformis HPV types (5, 8, 15, 20, 22, 24, 36, 37, 38, and 80) and putatively novel epidermodysplasia verruciformis HPV types (DL285, DL287, DL436, and alb-1, -2, -3, -5, -6, -7, -8, -10, -11, -12, and -13). HPV coinfection was frequent, found in 48% (two HPV genotypes in 35% and 3 in 13%). Of NS and EN, 42% had HPV genotypes associated with cancer (ie, HPV 5, 8, 16, 20, 33, and 38); the two most commonly identified HPV types where HPV 16 (39%) and HPV 38 (18%). No differences were detected comparing frequency of HPV DNA detected with respect to age or presence of a secondary tumor. Histologically, all NS and EN showed HPV-associated cytopathic effects (ie, perinuclear halos, altered keratohyaline granules). By in situ hybridization, 64% (18/28) were positive, showing a low-intensity, punctate nuclear signal in epidermal and adnexal keratinocytes, indicating viral integration and low viral genome copy number.

LIMITATIONS

Absence of adjacent, uninvolved normal-appearing skin control samples.

CONCLUSION

HPV DNA is prevalent in NS, and HPV 16, the most frequently detected genotype, appears to be integrated into the host genome. Whether HPV represents a commensal infection caused by localized cutaneous predisposition, or is an essential factor in the pathogenesis of NS is unknown. The high frequency of oncogenic HPV types implicates maternal transmission of HPV and infection of an ectodermal stem cell leading to an epigenetic mosaic and altered skin development manifested along Blaschko's lines.

Sebaceous Carcinoma Arising in Nevus Sebaceus of Jadassohn: A Clinicopathological Study of Five Cases

The authors report a small series of sebaceous carcinoma developing in nevus sebaceus of Jadassohn (also known as organoid nevus) and analyze similar cases reported in the literature. All of our patients were females (age range 57-71 years; median 60 years) who had the organoid nevus on the scalp, face, or nuchal area, the rest of which was recognized clinically and/or histologically. All sebaceous carcinomas manifested unquestionable architectural (asymmetry, invasive growth) and cytological features of a carcinoma (cellular and nuclear pleomorphism, plentiful atypical mitoses, necroses en masse), demonstrated unambiguous sebaceous differentiation in the form of mature sebocytes, and lacked other differentiations. The sebaceous carcinoma was always accompanied by other benign or malignant adnexal lesions such as sebaceoma, syringocystadenoma papilliferum, syringocystadenocarcinoma papilliferum, trichoblastoma, tricholemmoma, desmoplastic tricholemmoma, or syringoma. In three cases, prominent mucinous metaplasia of sweat ducts and glands was seen. In two of these cases, sweat ducts exhibited hyperplastic changes. The analysis of the previously published material and our cases indicates that sebaceous carcinoma arising in organoid nevus has a female predilection and tends to occur in elderly patients. It may involve any site where nevus sebaceus typically occurs. Clinically, the tumor presents as a solitary nodule, ulcerated tumor, or mass, often with a recent history of rapid growth. It may arise alone, but it occurs more frequently as part of multiple benign and malignant adnexal tumors. The lesion does not seem to be associated with Muir-Torre syndrome. The rest of organoid nevus is usually recognized both clinically and microscopically, although large tumors may overgrow and mask the nevus. The tumor seems to be a low-grade carcinoma in terms of clinical behavior.

Cutaneous leiomyosarcoma, trichoblastoma, and syringocystadenoma papilliferum arising from nevus sebaceus

A 54-year-old man presented with a recurrent swelling on the right occipital region of the scalp. Two months earlier, the patient had undergone an initial local excision of the lesion which had enlarged progressively over the previous 2 years on a hairless patch which had been present since birth. On examination, a 5 x 4-cm, pinkish, firm, ulcerated swelling was seen on the right occipital region with a scar running over it. The lesion was not fixed to the underlying bone and there was no regional lymphadenopathy. X-Ray of the skull was normal and no evidence of metastatic disease was identified. Wide local excision of the tumor was performed and it was sent for histopathologic examination. Specimens and slides of the earlier surgery performed elsewhere were also studied. The specimen of the initial surgery consisted of skin-covered tissue with an exophytic firm growth measuring 6 x 5 x 4 cm. The skin surface was rough with areas of ulceration. No necrosis was noted grossly. Microscopically, three distinct lesions were seen. One was a well-circumscribed tumor located in the superficial dermis with lobules of basaloid cell aggregates with peripheral palisading and with no epidermal connection. The lobules were surrounded by cellular fibrous tissue (Fig. 1). Unlike basal cell carcinoma, however, no cleft between the cellular aggregates and stroma was noted. Foci of pigmentation were seen within cellular lobules and these features were consistent with a diagnosis of tricho-blastoma. The second tumor was seen adjacent to the first, and consisted of duct-like structures and cystic spaces with papillary projections. These were lined by double-layered epithelium with stromal infiltration by plasma cells, which are features of syringocystadenoma papilliferum (Fig. 2). The third lesion was a spindle cell sarcoma which formed the major part of the lesion, diffusely infiltrating the dermis and subcutaneous tissue, elevating and ulcerating the overlying skin. The tumor consisted of interlacing fascicles of spindle cells with oval to elongated nuclei having finely dispersed chromatin and inconspicuous nucleoli. The tumor cells were seen encircling the sweat glands, without destroying them (Fig. 3). Nuclear pleomorphism was minimal, with a mitotic rate of 9-10 per high-power field. A small area of epidermal hyperplasia with acanthosis and papillomatosis overlying malformed highly placed sebaceous glands was the only evidence of a pre-existing nevus sebaceus. The status of the surgical margins was not clearly discernible. The wide excision specimen of the recurrent swelling consisted of a skin-covered nodule with ulceration, measuring 3 x 4 x 3 cm, with a gray-white whorled cut surface. No necrosis was noted grossly. Multiple sections showed only spindle cell sarcoma infiltrating the skin and subcutaneous tissue, morphologically similar to the earlier tumor, with ulceration of the overlying skin. The surgical margins were free from tumor. Immunohistochemical stains on the spindle cell sarcoma showed positive staining for smooth muscle actin (SMA) (Fig. 4), vimentin, epithelial membrane antigen (EMA), and S100. The tumor cells were negative for cytokeratin (CK), HMB45, desmin, glial fibrillary acidic protein (GFAP), CD34, and CD68. Correlating the histomorphology and immunohistochemical findings, a diagnosis of cutaneous leiomyosarcoma with tricho-blastoma and syringocystadenoma papilliferum arising on nevus sebaceus was made. The patient received postoperative radiotherapy and is disease free 8 months after diagnosis.

[Tumors associated with nevus sebaceous]

BACKGROUND

Nevus sebaceus (NS) is a congenital hamartomatous lesion, usually involving the scalp or the face. Various benign and malignant neoplasms can develop in association with NS, the most common being trichoblastoma, syringocystadenoma papilliferum, viral warts and basal cell carcinoma (BCC).

PATIENTS AND METHODS

We retrospectively examined the clinical and histopathological records of 15 NS cases with an associated tumor which were diagnosed between 1996 and 2004.

RESULTS

All cases were adults and 3 of them had more than one tumor. Six cases had BCC, which is a higher incidence of malignant tumor association with NS, than that reported in last years. Trichoblastoma was observed in 3 cases and was the most common benign tumor in our series. Filiform, hyperkeratotic, pigmented, pedunculated and/or eroded papulonodular changes were major clinical signs of secondary tumors on NS in our series.

CONCLUSION

Clinical features are not sufficient enough to make an exact diagnosis of benign or malignant secondary tumors. Though prophylactic excision for NS is done less in last years, especially adult patients should closely be followed for any new changes evoking tumor development on this congenital lesion.

[Evolution of sebaceous hamartoma: prospective pathologic study illustrated with a voluminous ear location]

After an exeresis of a sebaceous hamartoma of retroauricular area, histologic examination showed a trichoblastoma mimicking a basal cell carcinoma. So we realized a retrospective study with histologic examination of 24 cases of basal cell carcinoma after hamartoma. On 24 cases, 19 were not basal cell carcinoma, but trichoblastoma. So the study goes in the same direction of the world literature: hamartoma have a minimal risk of basal cell carcinoma transformation. Exeresis is indicated because of the risk of evolution to a hypertrophic tumour.

Desmoplastic trichilemmoma: a rare tumor of the eyelid

PURPOSE

To report an upper eyelid mass which proved to be a desmoplastic trichilemmoma.

METHODS

A 60-year-old man had a slowly enlarging upper eyelid mass. The tumor was excised. The pathologic evaluation of the tumor was centered on the differential diagnosis.

RESULTS

The clinical appearance of this lesion is nonspecific and can simulate a verruca, follicular keratosis, or basal cell carcinoma. Central desmoplasia, outer root sheath differentiation of the tumor cells, and CD34 positivity are the main characteristics that allow differentiation from basal cell carcinoma.

CONCLUSIONS

Proper recognition of a benign neoplasm that may be misdiagnosed as basal cell cancer can prevent aggressive surgical treatment.

Syringocystadenoma papilliferum: an unusual cutaneous lesion in a pediatric patient

We report a case of syringocystadenoma papilliferum, a rare cutaneous adnexal neoplasm, occurring synchronously in two distinct unusual locations in a 22-month-old child with lesions on the lower leg and back.

Ductal Carcinoma Arising from a Syringocystadenoma Papilliferum in a Nevus Sebaceus of Jadassohn

We present an example of ductal carcinoma connected to a syringocystadenoma papilliferum situated in a nevus sebaceus of Jadassohn on the scalp of a 22-year-old woman. The ductal carcinoma involved the entire thickness of the dermis and extended to the subcutaneous fat. Because syringocystadenoma papilliferum is considered a hamartoma with apocrine differentiation, the ductal carcinoma here described was interpreted as an apocrine ductal carcinoma. Syringocystadenocarcinoma papilliferum is an exceedingly rare neoplasm, most examples of which seem to have arisen in its benign counterpart, syringocystadenoma papilliferum. From a histopathologic point of view, syringocystadenocarcinoma papilliferum usually shows a papillary configuration similar to that of syringocystadenoma papilliferum. In contrast, the case here described a ductal carcinoma superficially connected to a syringocystadenoma papilliferum, but mostly composed of small ductal structures embedded in a desmoplastic stroma and involving the full thickness of the dermis. We review the literature about the malignant neoplasms arising in the nevus sebaceus of Jadassohn.

Sebaceous carcinoma arising from nevus sebaceus: a case report

BACKGROUND

Sebaceous carcinoma (SC) is a rare, aggressive, malignant tumor that is derived from adnexal epithelium of sebaceous glands that are distributed mostly in the skin of the head, neck, and hair-bearing regions of the body.

OBJECTIVE

To discuss the clinical and histologic features and the prognosis of the extraocular SC.

METHOD

We report a case of SCs of the scalp arising from a previous lesion clinically compatible with a nevus sebaceous. The lesion was surgically excised completely.

RESULTS

The postoperative course was free of complications, and the patient was clinically free of disease at her recent follow-up 2 years after treatment.

CONCLUSIONS

The absence of metastasis or cutaneous recurrence in our patient, notwithstanding the size of the lesion and its late removal, almost 25 years after the first signs of its growth, confirms a much improved prognostic behavior for extraocular SCs.

[Sebaceous hamartoma of Jadasshon: trichoblastoma mimicking basal cell carcinoma?]

The sebaceous hamartoma of Jadassohn is a congenital skin malformation usually appeared at birth or in early childhood. Many authors support the notion that early complete surgical excision is necessary to prevent the development of malignant neoplasms (especially basal cell carcinoma) after puberty. On the contrary, others in recent large series suggest that it is an histological misdiagnosis: the basal cell-carcinoma is in fact a trichoblastoma, basaloïd neoplasm, but non-malignant one. We have also asked anatomopathologist for proofreading slide previously described as basal cell carcinoma to research unknown trichoblastoma. During the period, 1982 to 1999, 80 sebaceous hamartoma of Jadassohn were excised and 19 basal cell carcinoma were found. The basal cell carcinoma diagnosis has been confirmed in two cases only. The others were pigmented trichoblastomas. So, trichoblastoma is the most common basaloïd tumor developed in sebaceous of hamartoma Jadassohn. Nevertheless, we should recommend surgical excision during the childhood because of best elasticity of tissue, especially on the scalp where it's mostly localized.

No evidence of deregulated patched-hedgehog signaling pathway in trichoblastomas and other tumors arising within nevus sebaceous

Nevus sebaceous is a congenital malformation of the skin within which a number of neoplasms showing adnexal differentiation may arise. Recently, deletions in the patched gene region were reported in nevus sebaceous and constitutive activation of the patched-hedgehog signaling pathway was implicated in the development of tumors arising within nevus sebaceous. To substantiate further a role of the patched-hedgehog signaling pathway in secondary tumors arising within nevus sebaceous, we examined 11 nevus sebaceous associated with secondary tumors for loss of heterozygosity of the patched gene region by microsatellite polymerase chain reaction and patched mRNA expression by in situ hybridization. Unexpectedly, however, none of the tumors (including eight trichoblastomas) and nevus sebaceous lesions showed loss of heterozygosity at any polymorphic loci close to the patched gene. Further more, none of the nevus sebaceous lesions and secondary tumors gave detectable signals for patched mRNA. In contrast, four of 11 sporadic basal cell carcinomas, that were examined for comparison, showed loss of heterozygosity at the patched gene locus (p <0.05), and moderate to strong signals for patched mRNA was observed in all seven basal cell carcinoma tumors examined (p <0.0001). Additional investigation by reverse transcription-polymerase chain reaction in four basal cell carcinomas and two nevus sebaceous tumors also showed the expression of Gli-1, another target gene in the patched-hedgehog signaling pathway, in all the basal cell carcinomas samples but not in any of the nevus sebaceous tumors examined. The findings in this study do not support the view that the deregulation of the patched-hedgehog signaling pathway is involved in the pathogenesis of nevus sebaceous and associated tumors, and show that, although morphologically similar, trichoblastomas and basal cell carcinomas have a different molecular pathogenesis.

Sebaceous carcinoma, trichoblastoma, and sebaceoma with features of trichoblastoma in nevus sebaceus

A 73-year-old woman had a linear yellowish plaque on the upper part of her right ear since birth. She presented because of the sudden growth of a nodule within the plaque. The plaque was waxy and yellowish, arching around the upper part of the ear. A reddish to yellowish large nodule was seen within the central part of the arc-shaped plaque; in addition, a small pigmented nodule, a small skin-colored nodule, and a few pigmented papules were observed in the anterior half of the arched plaque. Histopathologic examination revealed the large nodule to be sebaceous carcinoma, the small pigmented nodule to be trichoblastoma, the small skin-colored nodule to be sebaceoma with the features of trichoblastoma, a few pigmented papules to be superficial trichoblastomas due to primitive follicular induction, and the linear yellowish plaque to be nevus sebaceus. Although our literature search revealed scanty reports of definite cases of sebaceous carcinoma in nevus sebaceus, the presented case demonstrated the occurrence of sebaceous carcinoma in nevus sebaceus. Malignant neoplasms occurring in nevus sebaceous seem to be extremely rare, but care should be taken when a large nodule suddenly grows in a lesion of nevus sebaceus, especially in older adults. The presented case also suggested a close relation between trichoblastoma and sebaceoma. The cytokeratin staining pattern could not distinguish between sebaceous and follicular neoplasms in our case.

Clear cell trichoblastoma in association with a nevus sebaceus

Nevus sebaceus is a hamartoma that is frequently associated with various neoplasms. Among the neoplasms observed in sebaceus nevi, trichoblastomas are the most common. The present case, to my knowledge, is the first description of a clear cell variant of trichoblastoma.