Role of immunohistochemistry in diagnosing tumors of cutaneous appendages

The 2023 WHO updates on skin tumors: advances since the 2018 edition

Pathology is pivotal in diagnosing skin tumors, and the precision of diagnosis is crucial to devise customized treatment plans and enhance patient care in dermatology. The latest edition of the World Health Organization's classification of skin tumors serves as a comprehensive compendium, summarizing and categorizing all recent advancements in both anatomical-pathological and molecular aspects of cutaneous neoplasms. Several relevant advances have been introduced and new entities have been described. While the fundamental structure of the classification remains unchanged, notable additions include three new sections aimed at providing a more exhaustive description of skin lesions: nail unit tumors, skin metastases, and genetic tumor syndromes associated with skin malignancies. Recent strides in molecular pathology have led to significant breakthroughs in decoding the underlying mechanisms of various skin tumors, ranging from adnexal neoplasms to hematolymphoid neoplasms, soft tissue tumors, and melanocytic lesions. Of particular importance is the evolution in our understanding of melanocytic neoplasms, with the introduction of the term "melanocytoma" reserved for lesions exhibiting "intermediate" biological behavior and characterized by specific molecular mutations. The pathologic diagnosis process integrates morphological, immunohistochemical, and molecular features, playing a crucial role in clinical decision-making. The WHO classification serves as a valuable tool in promoting multidisciplinarity in the management of cutaneous neoplasms with the aim of translating novel pathological discoveries into more effective treatments. This review aims to distill the major updates introduced by the new classification, providing a synthesis of the latest scientific insights.

Localized Hidradenocarcinoma of the Scalp: A Case Report

Hidradenocarcinomas or malignant hidradenomas are tumors developed from the sweat glands, in particular, the eccrine glands. It is a rare entity of skin tumors and frequently appears de novo with a slight female predominance and an average age of 50 years at diagnosis. We report the case of a 57-year-old woman treated for localized hidradenocarcinoma of the scalp, successfully managed by surgery and adjuvant radiotherapy.

Evidence-Based Clinical Practice Guidelines for Microcystic Adnexal Carcinoma: Informed by a Systematic Review

IMPORTANCE

Microcystic adnexal carcinoma (MAC) occurs primarily in older adults of white race/ethnicity on sun-exposed skin of the head and neck. There are no formal guiding principles based on expert review of the evidence to assist clinicians in providing the highest-quality care for patients.

OBJECTIVE

To develop recommendations for the care of adults with MAC.

EVIDENCE REVIEW

A systematic review of the literature (1990 to June 2018) was performed using MEDLINE, Embase, Web of Science, and the Cochrane Library. The keywords searched were microcystic adnexal carcinoma, sclerosing sweat gland carcinoma, sclerosing sweat duct carcinoma, syringomatous carcinoma, malignant syringoma, sweat gland carcinoma with syringomatous features, locally aggressive adnexal carcinoma, and combined adnexal tumor. A multidisciplinary expert committee critically evaluated the literature to create recommendations for clinical practice. Statistical analysis was used to estimate optimal surgical margins.

FINDINGS

In total, 55 studies met our inclusion criteria. The mean age of 1968 patients across the studies was 61.8 years; 54.1% were women. Recommendations were generated for diagnosis, treatment, and follow-up of MAC. There are 5 key findings of the expert committee based on the available evidence: (1) A suspect skin lesion requires a deep biopsy that includes subcutis. (2) MAC confined to the skin is best treated by surgery that examines the surrounding and deep edges of the tissue removed (Mohs micrographic surgery or complete circumferential peripheral and deep margin assessment). (3) Radiotherapy can be considered as an adjuvant for MAC at high risk for recurrence, surgically unresectable tumors, or patients who cannot have surgery for medical reasons. (4) Patients should be seen by a physician familiar with MAC every 6 to 12 months for the first 5 years after treatment. Patient education on photoprotection, periodic skin self-examination, postoperative healing, and the possible normal changes in local sensation (eg, initial hyperalgesia) should be considered. (5) There is limited evidence to guide the treatment of metastasis in MAC due to its rarity. Limitations of our findings are that the medical literature on MAC comprises only retrospective reviews and descriptions of individual patients and there are no controlled studies to guide management.

CONCLUSIONS AND RELEVANCE

The presented clinical practice guidelines provide an outline for the diagnosis and management of MAC. Future efforts using multi-institutional registries may improve our understanding of the natural history of the disease in patients with lymph node or nerve involvement, the role of radiotherapy, and the treatment of metastatic MAC with drug therapy.

MYB, CD117 and SOX-10 expression in cutaneous adnexal tumors

BACKGROUND

Elevated MYB expression has been documented in adenoid cystic carcinoma (ACC), cylindroma, and spiradenoma, but the specificity of this finding is unknown. CD117 and SOX-10 expression also occurs in some cutaneous adnexal tumors. This study assesses MYB, CD117 and SOX-10 expression in cutaneous adnexal tumors.

METHODS

Retrospective analysis of 184 benign adnexal tumors (140 eccrine/apocrine, 40 follicular and 10 sebaceous), and 30 malignant adnexal tumors was performed with MYB, SOX-10 and CD117 immunostaining.

RESULTS

In the benign adnexal tumors, 16% (23/140) significantly expressed MYB. MYB expression was limited to cylindromas and to a lesser extent, spiradenomas in the benign cohort. Elevated MYB expression was detected in mucinous carcinoma, endocrine mucin-producing sweat gland carcinoma and 1 and 4 cases of extramammary Paget's disease (EMPD) in the malignant cohort. CD117 and SOX-10 had similar overall positivity rates in benign apocrine and eccrine tumors (45% and 68% respectively), and were generally negative in other benign and malignant adnexal tumors.

CONCLUSION

Expression of MYB appears limited to a small number of cutaneous adnexal tumors, including cylindromas, spiradenomas, ACCs, mucinous carcinoma, endocrine mucin-producing sweat gland carcinoma and some cases of EMPD.

Primary Cutaneous Mammary Analog Secretory Carcinoma With ETV6-NTRK3 Translocation

Mammary analog secretory carcinoma (MASC) is a recently described tumor of the salivary glands named for its morphological and molecular similarity to secretory carcinoma of the breast. Many primary carcinomas arising from the adnexal glands also share similar morphology to those arising from the breast. Brandt et al first described primary cutaneous MASC in 2009 and since then only 2 other cases have been reported. Herein, we describe a long-standing mass on the arm of an otherwise healthy 40-year-old female. Histologic examination revealed a circumscribed but unencapsulated, nodular tumor composed of bland epithelial cells arranged in solid and microcystic growth patterns. The cells showed vacuolated cytoplasm and round to oval nuclei with vesicular chromatin. Intraluminal homogenous eosinophilic secretions were present. Mitotic figures were not identified. The tumor cells stained positive for CK8/18, CK7, and S100 but were negative for other markers performed, including estrogen receptor, progesterone receptor, HER2/neu, paired box 8 (PAX8), and thyroid transcription factor 1 (TTF1). As the patient clinically had no other masses or known carcinomas, a diagnosis of primary cutaneous MASC was rendered. The ETV6-NTRK3 fusion transcript was subsequently detected by reverse transcriptase polymerase chain reaction amplification, further supporting the diagnosis. We present this case to review the histologic features of MASC and highlight the importance of recognizing this lesion not only as a possible cutaneous metastasis but also as a primary cutaneous tumor.

Challenges in the diagnosis of cutaneous adnexal tumours

The diagnosis of cutaneous adnexal neoplasms, a heterogeneous group of entities, is often perceived by practising pathologists as challenging. A systematic approach to diagnosis is necessary for classification of these lesions, which establishes the tumour differentiation (follicular, sebaceous, sweat gland or apocrine) and evaluates histological features differentiating between benign and malignant entities. Consideration of clinical history is a necessary adjunct in evaluation of the adnexal neoplasm, as characteristic anatomical sites are described for many adnexal lesions. In some instances, immunohistochemical studies may also be employed to aid the diagnosis. The differential diagnosis between primary cutaneous adnexal neoplasms and cutaneous metastases from visceral tumours may also be difficult. Clinical, radiological, histological and immunohistochemical characteristics will be further discussed, considering that the correct diagnosis has a significant impact on the patient's management and prognosis.

Basal cell carcinomas showing histological features generally associated with cutaneous adnexal neoplasms

Basal cell carcinoma (BCC) is the commonest malignant neoplasm in humans. Although a histopathological diagnosis of BCC is straightforward in the vast majority of cases, unusual histological variants can present a diagnostic challenge. A small proportion of BCCs show features which are generally associated with cutaneous adnexal neoplasms. Such changes may involve either the epithelium or the stroma and can mislead the pathologist particularly in small biopsies. Despite the growing evidence which speculate that BCC is a primitive follicular tumor, it is unusual to encounter tumors which actually show definitive signs of adnexal differentiation. This review aims to address this somewhat overlooked aspect of a very common tumor and offers practical guidance to distinguish them from adnexal neoplasms which they might mimic.

Cytomorphology of sebaceous carcinoma with analysis of p40 antibody expression

BACKGROUND

Sebaceous carcinomas (SBCs) are aggressive tumors with the potential to cause great morbidity and mortality. Poorly-differentiated tumors may at times pose challenges for the correct diagnosis. p40, a new antibody that targets a short isoform of p63 has been shown as a promising squamous cell marker. In this study, we sought to evaluate cytomorphological features of SBC and p40 expression analysis.

METHODS

A total of 29 previously diagnosed cases of SBCs including fine-needle aspirates and histopathology specimens from various sites were reviewed and studied for p40 expression. p40 nuclear expression was semi-quantitatively assessed. Adequate positive and negative controls of non-small cell lung carcinoma were taken for comparison. Expression pattern of normal sebaceous glands was also analyzed.

RESULTS

Of the 29 cases, 13 (44.8%) were from the periocular region. The most common extraocular site was parotid gland. Morphologically tumors were categorized into well- and poorly-differentiated varieties based on extent of sebaceous differentiation. p40 positivity was seen in all cases of cytology aspirates and histology sections with similar intensity. No difference in percentage positivity of cells was recorded in well- and poorly-differentiated tumors.

CONCLUSION

p40 can be a valuable marker when evaluating tumors with possible sebaceous differentiation. Although p40 expression in SBCs is not as useful for the differential diagnosis that includes poorly-differentiated squamous cell carcinoma, this study, for the first time in the literature, highlights an important observation that p40 can be utilized as a marker for sebaceous lineage.

Perilipin and adipophilin expression in sebaceous carcinoma and mimics

Although adipophilin has been reported to be a sensitive marker for sebaceous carcinoma, others have noted its expression in squamous cell carcinoma and a variety of noncutaneous tumors, suggesting that lipid droplet accumulation is a frequent feature of neoplastic cells. We investigated the expression of adipophilin and perilipin in 101 cutaneous carcinomas. They included 30 cases of sebaceous carcinoma, 28 squamous cell carcinoma with clear cell change (18 invasive and 10 in situ tumors), 8 hidradenocarcinomas, 1 spiradenocarcinoma, 10 porocarcinomas, 4 malignant chondroid syringomas, 1 malignant cylindroma, 7 apocrine carcinomas, 6 eccrine carcinomas, 5 aggressive digital papillary adenocarcinomas, and 1 pilomatrical carcinoma. Adipophilin stained the rim of cytoplasmic lipid droplets in various tumor types, including sebaceous carcinomas (30/30, 100%), squamous cell carcinoma with clear cell change (21/28, 75%), and eccrine-apocrine carcinomas (25/43, 58%). On the other hand, perilipin expression was seen in 13 (43%) of 30 sebaceous carcinoma and only 1 hidradenocarcinoma. The remaining 28 squamous cell carcinomas with clear cell change and 42 eccrine-apocrine carcinomas were negative. Although specific for invasive sebaceous carcinoma, perilipin expression was not helpful in distinguishing sebaceous carcinoma in situ from squamous cell carcinoma in situ with clear cell change. The expression of adipophilin seen in variety of cutaneous tumors suggests that the biosynthesis of lipid is altered in these neoplasms.