Benign cutaneous adnexal tumors with combined folliculosebaceous, apocrine, and eccrine differentiation. Clinicopathologic and immunohistochemical study of eight cases

A Rare Hybrid Skin Cyst of the Scalp With Pilar and Apocrine Features

Benign epithelial skin cysts containing multiple components of the folliculo-sebaceous apocrine unit are only rarely reported in the literature. Here, we describe a 12-year-old girl who presented with a cystic mass on the vertex of her scalp. Upon resection, it showed a hybrid benign skin cyst with interesting histological features of both pilar and apocrine differentiation. The clinicopathological and imaging findings of this unusual skin cyst, successfully managed by a plastic surgeon and neurosurgeon, are described. Pathologists and clinicians should be aware of this type of skin cyst rarely encountered in their clinical practice.

Trichilemmal Cysts With Divergent Ductal Differentiation: A Series of 4 Cases

ABSTRACT

Trichilemmal cysts are common clonal tumors with a predilection for the scalp. They are composed of an outer epithelial wall resembling the outer root sheath in the isthmus of the hair follicle and a central core of compact keratin. Sweat duct differentiation is exceptional with only one convincing case reported to date. Here, we sought to characterize the clinicopathological characteristics of sweat duct differentiation in trichilemmal cysts. We reviewed all cases of trichilemmal cyst diagnosed at our institution between 2008 and 2019. Ductal structures were found in 4 of 411 cases (0.97%). Subjects included 2 male and 2 female patients with a median age of 37.5 years (range 34-55). The ducts were lined by attenuated epithelial cells and immunoreactive for polyclonal carcinoembryonic antigen and cytokeratin 7. Ductal differentiation involved a median of 7.5% (range 1%-50%) of the cyst wall. All 4 cases were from the scalp and treated with local excision. No recurrence was identified with a median follow-up period of 1.5 years (range 1-12 years). In summary, sweat duct differentiation in trichilemmal cysts is rare but likely under recognized. Conceptually, we suggest it represents a type of divergent cellular differentiation within a clonal neoplasm rather than a retention cyst or hybrid cyst.

Atypical Facial Chondroid Syringoma, A Rare Clinical Entity: Case Report with Review of Literature

Chondroid syringoma (CS) is a rare mixed tumor of sweat gland origin with a reported incidence of less than 0.1%. The tumor is mostly benign and usually seen in males. It comprises of both epithelial and mesenchymal elements. The usual presentation and clinical course of this condition makes it liable to be confused with other commoner skin conditions. We hereby present a case of facial CS in a young female patient.

Cyto-Histopathological Correlation of Skin Adnexal Tumors: A Short Series

Background:

Skin adnexal neoplasms are relatively rare and thus uncommonly encountered in routine pathology practice.

Aims:

The present study was conducted with the aim to diagnose various skin adnexal tumors on fine-needle aspiration cytology (FNAC) followed by confirmation on histopathology and immunohistochemistry of the excised tumor.

Materials and Methods:

A total of 11 cases of superficial nodular swellings of the skin were studied over a period of 2 years from 2015 to 2016. FNAC of the swelling was performed and slides were stained with Giemsa stain. Following FNAC, the swelling was excised and subjected to histopathological examination. Immunohistochemistry was performed in some cases for confirmation.

Results:

It was observed that overall incidence of adnexal tumors (ATs) encountered on FNAC was very low. Typing of ATs on cytology was possible in 82% cases (9/11 cases) with diagnostic accuracy of 88% (8/9 cases). Most common tumor encountered in the study was nodular hidradenoma followed by pilomatrixoma, trichoepithelioma, cylindroma, chondroid syringoma, and trichilemmal cyst. Majority of the cases were benign except one case, which subsequently turned malignant.

Conclusion:

FNAC is a simple, safe, and cost-effective tool in diagnosing skin ATs. Cytological diagnosis of these lesions is depends on clinical correlation and cytomorphological features. FNAC in lesions suspected to be malignant can guide the surgeon regarding extent of excision.

Eccrine spiradenoma: A rare adnexal tumor

Eccrine spiradenoma is one of the rare adnexal tumors with eccrine differentiation; however, it is considered to have apocrine differentiation. Around 50 cases of eccrine spiradenoma have been reported in the literature. Due to vascularity and painful symptoms, it is often confused with the painful lesions of skin such as glomus tumor and angioleiomyoma. Surgical excision is considered the gold standard for the treatment of these cases, with low rates of recurrence. Here, we present a 52-year-old male who presented with a nodular lesion in the left side of chest for the past 4 years. Surgical excision was performed and the tissue was sent for histopathological examination. Eccrine Spiradenoma may present congenitally or spontaneously as tumor of the sweat glands with unclear etiology. Early accurate diagnosis is very important in preventing chances of recurrence and more importantly identifying onset of malignant transformation.

Sebaceous Neoplasms

Sebaceous skin tumors are classified into sebaceous adenoma, sebaceoma, and sebaceous carcinoma. An additional group of cystic sebaceous tumors indicate the Muir-Torre syndrome (MTS). Cystic sebaceous tumors are considered as morphologic variants of the 3 main categories. Multilineage adnexal tumors with partly sebaceous differentiation may pose a challenge to categorize. Sebaceous hyperplasia and nevus sebaceus are not considered as true sebaceous tumor entities. Recently, attention has been drawn to morphologic clues of sebaceous differentiation. Immunohistochemistry using the mismatch repair proteins and/or genetic microsatellite instability testing should be performed on sebaceous neoplasms to diagnose MTS as early as possible.

Adnexal Tumors of Skin: An Experience at a Tertiary Care Center at Delhi

Background:

Adnexal skin tumors are a heterogeneous group of uncommon tumors usually misdiagnosed clinically due to a huge variety of types and their variants. Histopathology usually helps in establishing the diagnosis.

Aims:

The study was undertaken to analyze the morphological, clinical, and histological features of adnexal tumors (ATs) of the skin at our center over a period of 4 years.

Subjects and Methods:

retrospective study was conducted over a period of 4 years (April 2010–March 2014), comprising 25 ATs of skin diagnosed in the Department of Pathology, Hamdard Institute of Medical Sciences and Research, Jamia Hamdard, New Delhi. All the consecutively reported AT cases were reviewed and reclassified as AT arising from sebaceous glands, hair follicles, or sweat glands. The concordance of clinical and histopathological diagnosis was also assessed.

Results:

Most of the ATs were benign (24/25) with head and neck being the most common location (72%). Nearly 56% of the tumors exhibited sweat gland differentiation, 28% hair follicle differentiation, and sebaceous gland tumors accounted for 16%. The most common varieties of tumors encountered in the present study included hidradenoma papilliferum and pilomatricoma. The concordance between clinical and histopathological diagnosis was found to be 50% approximately.

Conclusions:

ATs of the skin are rare neoplasms with benign tumors being far more common. They are often misdiagnosed clinically, so histopathology remains the gold standard for establishing an accurate diagnosis of skin ATs.

GATA3 and MYB Expression in Cutaneous Adnexal Neoplasms

Knowledge of staining pattern of certain immunostains might be useful in the classification of cutaneous adnexal tumors that can have clinical importance. We studied GATA3 and MYB expression in archival materials of 220 adnexal tumors comprised of sebaceous carcinomas, follicular tumors, apocrine carcinoma, predominantly apocrine tumors, predominantly eccrine tumors, and others including adenoid cystic carcinomas. Nuclear GATA3 expression was seen in 70% (153/220) of cases, including sebaceous carcinoma (93%), apocrine carcinoma (93%), follicular neoplasms (100%), and predominantly apocrine neoplasms (69%), yet only 38% of predominantly eccrine neoplasms. Nuclear MYB expression was seen in 43% (81/188) of cases, including adenoid cystic carcinoma (90%), predominantly apocrine tumors (66%), follicular neoplasms (49%), apocrine carcinomas (14%), predominantly eccrine tumors (11%), and sebaceous carcinomas (4%). GATA3 and MYB expression were noted in 43% (9/21) and 24% (5/21) of cutaneous metastases, respectively. Expression of both GATA3 and MYB was noted in 33% (60/184) of primary adnexal tumors versus 19% (4/21) of cutaneous metastases. GATA3 preferentially labels tumors with follicular, sebaceous, and apocrine differentiation. MYB is potentially a helpful stain in the distinction of desmoplastic trichoepithelioma versus basal cell carcinoma. The coexpression of GATA3 and MYB might be helpful in the distinction of primary cutaneous adnexal carcinoma versus metastatic breast, salivary gland, or urothelial carcinoma.

A Rare Case of a Pilar Cyst With Ductal Differentiation

Pilar cysts are common squamous-lined cysts that typically occur on the scalp. They are believed to arise from the isthmus of anagen hairs or from the sac surrounding catagen and telogen hairs. The authors describe a rare case of a pilar cyst with prominent ductal differentiation, presumably of eccrine derivation. Sweat duct differentiation has been described in a myriad of cutaneous neoplasms and rarely within epidermoid cysts. The authors could only find one other case in the literature describing a pilar cyst with sebaceous and apocrine differentiation. The clinicopathologic findings are described here.

Differential diagnosis of eccrine spiradenoma: A case report

Eccrine spiradenoma (ES) is a rare, benign adnexal neoplasm that may easily be mistaken for glomus lesions or angioleiomyoma due to its painfulness and florid vascularization. A 44-year-old male with a blue-colored, nodular tumor on the left knee, present for 10 years, was submitted for diagnosis. Dermatological examination was undertaken, followed by surgical excision of the subcutaneous lesion and histopathological examination of the tissue. Subjective symptoms included tenderness upon palpation and routine investigations were within normal limits. Immunohistochemical analysis of the tumor cells demonstrated positive staining for CK5/CK6, CK8/CK18, S100, as well as small vacuole-like positive for EMA, and was therefore diagnosed as ES. The results of the present study suggest that immunohistochemical assays may be helpful to clarify the diagnosis and differentiate ES from other painful subcutaneous tumors exhibiting similar clinical and histological presentations.

A clinico-histopathological study of appendageal skin tumors, affecting head and neck region in patients attending the dermatology opd of a tertiary care centre in eastern India

Introduction:

Appendageal skin tumors (ATs) are those neoplasms that differentiate toward/arise from pilosebaceous apparatus, apocrine, or eccrine sweat glands. Pilosebaceous apparatus are concentrated in head–neck area; thus it is expected that ATs would account for a major fraction of skin tumors over this site.

Aims:

This study aims at finding the clinico-histopathological correlation in cases ATs in head–neck region among attendees of dermatology OPD.

Materials and Methods:

Cross-sectional descriptive study, conducted over 1-year period. All clinically suspected cases of ATs were evaluated and subjected to histopathological examination. Confirmed cases of ATs were finally analyzed.

Results

Among twenty eight thousand four hundred sixty six new patients attending OPD, 30 suspected cases of ATs underwent histopathological examination. Histopathology was confirmatory in only 23 (76.67%) cases. Out of 23, syringoma were found in 9 (39.13%), trichoepithelioma in 6 (26.08%), syringocystadenoma papilliferum in 4 (17.39%), sebaceous gland hyperplasia in 3 (13.04%), and vellous hair cyst in 1 (4.34 %). Females (65.21%) outnumbered males (34.78%) in our study population.

Conclusions:

ATs of head–neck region constitute a meager population (0.08%) attending dermatology OPD, and were more common among young population. Often it is over-diagnosed clinically thus necessitating histological confirmation. Young females being cosmetically more conscious are more eager to seek advice for this condition.

Apocrine mixed tumor of the skin (“mixed tumor of the folliculosebaceous-apocrine complex”)

BACKGROUND

A systematic analysis of the entire spectrum of various forms of differentiation and metaplastic epiphenomena in cutaneous apocrine mixed tumor (AMT) has never been performed.

OBJECTIVE

The purpose of our study was to study a large number of cutaneous mixed tumors so as to fully characterize the entire spectrum of differentiations and metaplastic changes that may occur in the epithelial, myoepithelial, and stromal components of AMT.

METHODS

This article reports a light-microscopic study of 244 cases of cutaneous AMT, complemented by a literature review.

RESULTS

All types of differentiation along the lines of the folliculosebaceous-apocrine unit can be seen in AMT. The spectrum of metaplastic changes in the epithelial components includes squamous metaplasia, mucinous metaplasia, oxyphilic metaplasia, clear cell change, columnar metaplasia, hobnail metaplasia, and cytoplasmic vacuolization. The following changes in the myoepithelial component were documented: clear cell change, hyaline cells, plasmacytoid cells, spindling, and collagenous spherulosis. Stromal alterations included chondroid metaplasia, osseous metaplasia, and adipose metaplasia.

LIMITATIONS

This study utilizes tissue specimens that mainly came as consultations; therefore some inherent selection bias exists.

CONCLUSIONS

AMT displays a wide range of differentiation and metaplastic changes in its epithelial, myoepithelial, and stromal components. These phenomena are not mutually exclusive. When unduly prominent, they may present diagnostic pitfalls. Our findings corroborate those of previous publications, stressing the remarkable diversity of differentiation and metaplasias that may be found in cutaneous AMT. We propose that the most appropriate name for these lesions is "mixed tumor of the folliculosebaceous-apocrine complex."

Cutaneous Sebaceous Neoplasms With a Focal Glandular Pattern (Seboapocrine Lesions): A Clinicopathological Study of Three Cases

Presented here are three cutaneous sebaceous tumors (one carcinoma and two sebaceomas), each demonstrating a focal glandular pattern representing apocrine differentiation. The patients, two males and one female, each clinically presented with a small solitary nodule or tumor on the scalp. None of the patients had features of Muir-Torre syndrome. Surgical removal of the lesions was performed in all cases. None of the patients developed recurrence or metastasis after surgery (follow-up ranged from 18 to 24 months). The glandular areas represented a minor but significant component of the lesions and appeared as glands of various complexity, mostly as simple round or elongated tubular structures lined by a row of cuboidal to columnar cells with eosinophilic cytoplasm and round nuclei, with or without a distinct nucleolus. Decapitation secretion was evident but not prominent. In both sebaceomas, at least a portion of the glands had a peripheral small-cell layer that appeared similar to the basal/myoepithelial cells of normal eccrine and apocrine ducts. In some glands, the basal/myoepithelial cells seemed to have undergone hyperplasia, resulting in two or more rows of cells that even formed small islands, with an overall appearance reminiscent of basal cell hyperplasia in the prostate, arising in the basal layer of the prostatic glands. The descriptive terms seboapocrine carcinoma or seboapocrine sebaceoma are proposed for such lesions. These tumors may be viewed as rare histopathological variants of sebaceous carcinoma and sebaceoma, with a second type of differentiation along the lines of the folliculosebaceous-apocrine unit.

Skin adnexal neoplasms--part 2: an approach to tumours of cutaneous sweat glands

Tumours of cutaneous sweat glands are uncommon, with a wide histological spectrum, complex classification and many different terms often used to describe the same tumour. Furthermore, many eccrine/apocrine lesions coexist within hamartomas or within lesions with composite/mixed differentiation. In addition to the eccrine and apocrine glands, two other skin sweat glands have recently been described: the apoeccrine and the mammary-like glands of the anogenital area. In this review (the second of two articles on skin adnexal neoplasms), common as well as important benign and malignant lesions of cutaneous sweat glands are described, and a summary for differentiating primary adnexal neoplasms from metastatic carcinoma is outlined, striving to maintain a common and acceptable terminology in this complex subject. Composite/mixed adnexal tumours are also discussed briefly.

Low-grade Adnexal Carcinoma of the Skin With Multidirectional (Glandular, Trichoblastomatous, Spiradenocylindromatous) Differentiation

The conjoint occurrence of follicular, sebaceous, or apocrine differentiations in a cutaneous adnexal neoplasm is a known event, more often encountered in benign neoplasms, whereas reports of cutaneous malignant adnexal tumors with bilineage or trilineage differentiation are few. A new case of a cutaneous malignant adnexal neoplasm with multidirectional differentiation is reported here. A 57-year-old woman presented with a long-standing, slowly growing, asymptomatic solitary tumor the size of a large nut in the coccygeal area, which was surgically excised. Ten years after the surgery, there was no evidence of recurrence or metastasis. Microscopically, the neoplasm was located in the dermis with focal extension into the subcutis. It was asymmetric, horizontally oriented, and mostly composed of small nodules that varied in shape from round and oval aggregations to elongated strands and irregular islands; the nodules were either clustered, formed a jigsaw puzzle-like pattern or were dispersed. The nodules were composed of small basaloid cells sometimes intermixed with larger cells with ample cytoplasm forming glandular structures. Rare nodules resembled elements seen in a spiradenoma by containing scattered lymphocytes and globules of hyalinized eosinophilic basal membrane material. The stroma was paucicellular, but focally it resembled that seen in perifollicular mesenchyme. Mitotic figures, including abnormal ones, were infrequent, but mild nuclear pleomorphism, nuclear crowding, and individual cell necrosis were easily appreciable in both small basaloid cells and cells with clear cytoplasm. Perineural invasion was apparent. We classified this tumor as a well-differentiated adnexal carcinoma demonstrating combined follicular and apocrine differentiation. It differs from previously published cases of malignant adnexal tumors with multidirectional differentiation and further exemplifies the spectrum of diversity encountered in malignant proliferations with differentiation toward the folliculosebaceous-apocrine unit.

Basal cell carcinomas with unusual histologic patterns

Uncommon histologic variants of basal cell carcinoma (BCC) can present a diagnostic challenge. In this case series, we describe 3 patients with unusual BCCs encountered in a dermatologic surgical unit over a 1-year period from September 2003 to September 2004. The formalin-fixed, paraffin-embedded histologic specimens were initially examined microscopically after staining with hematoxylin and eosin. Additional stains, including diastase periodic acid-Schiff, colloidal iron, carcinoembryonic antigen, and cytokeratin-20, were subsequently performed as appropriate. Of the 3 lesions, one exhibited apocrine differentiation and two demonstrated a trabecular growth pattern. Although BCCs demonstrating apocrine differentiation have previously been described, a trabecular growth pattern, to our knowledge, has not been previously reported for BCC.

Trichoblastoma with Apocrine and Sebaceous Differentiation

Trichoblastoma is a rare, benign tumor that differentiates toward the hair germ, the embryonic precursor of a hair follicle. Several cases of trichoblastoma showed multiple differentiation toward more than one type of adnexal structure. We report a case of a trichoblastoma, which had developed on the scalp as a solitary 1-cm nodule 3 years ago. A histologic examination indicated that the specimen had features of multiple differentiation. In particular, there were occasional foci of decapitation secretion, as well as cells with web-like and bubbly cytoplasm suggesting seboblasts, and a sebaceous duct-like structure. In addition, there were occasional germinative cells in the palisade, and scattered hair papilla-like structures showing follicular differentiation. An immunohistochemical study showed that the neoplasm, or areas in it, stained positive for low molecular cytokeratin, high molecular cytokeratin, EMA, S-100, and GCDFP-15. This is an unusual case of a trichoblastoma with apocrine and sebaceous differentiation.

Fine-needle aspiration biopsy of a cystic pleomorphic adenoma with extensive adnexa-like differentiation: differential diagnostic pitfall with mucoepidermoid carcinoma

Although fine-needle aspiration biopsy (FNAB) is a highly accurate tool for the diagnosis of pleomorphic adenomas, even this common salivary gland neoplasm can be diagnostically challenging and cause pitfalls in cytodiagnosis. In particular, the presence of either cystic degeneration or squamous and mucinous metaplasia can lead to a false positive diagnosis of malignancy. Here we present the case of a 16-year-old female who presented with a painless, slowly growing mass in the superficial lobe of the right parotid gland. Magnetic resonance imaging of the parotid demonstrated a mass with heterogeneous postcontrast enhancement and a central, nonenhancing area suggestive of necrosis. FNAB of the lesion yielded proteinaceous debris and numerous whorls of keratin, small cohesive clusters of basaloid and squamoid epithelial cells, and many vacuolated and foamy cells. Initially and after consultation at an outside institution, the FNAB was reported as an "atypical neoplasm, cannot exclude mucoepidermoid carcinoma." A total, nerve-sparing parotidectomy and level II neck dissection revealed a pleomorphic adenoma with central cystic degeneration and extensive mixed appendageal differentiation. While foci of squamous metaplastic changes may occur in pleomorphic adenomas, the combination of cystic degeneration and extensive appendageal differentiation with numerous keratotic cysts is rare, and it presents the potential for misinterpretation of the FNAB as indicative of malignancy in general, and mucoepidermoid carcinoma in particular.

A tumor with composite pilo-folliculosebaceous differentiation harboring a recently described new entity--melanocytic matricoma

We report on a case of a peculiar tumor of the pilosebaceous unit showing a composite histologic appearance. The case presented as a pigmented crusted lesion on the back of the nose of a 62-year-old woman with markedly sun-damaged skin. Histologically, the superficial portion of the neoplasm was composed of buds and nests of basaloid epithelium with varying degrees of pilar and sebaceous differentiation. Adjacent to this component, lobules of squamous cells with cytoplasmic glycogenation suggesting the mature outer root sheath were seen. In the underlying dermis, there was a well-defined nodular proliferation composed of variably pigmented basaloid matrical cells forming clusters of "shadow" or "ghost cells" admixed with numerous melanized dendritic melanocytes; this last component of the neoplasm was identical to a recently described entity, melanocytic matricoma. The small size, circumscription, and absence of necrosis favored benignity, although the cytologic atypia of matrical cells did not exclude malignancy. The case is interesting not only because it is the third reported case of a peculiar neoplasm imitating the epithelial-melanocytic interaction in the embryonal hair follicle or bulb of the anagen follicle but because the part resembling melanocytic matricoma presented as a component of a complex lesion. We believe that sunlight may have played a role in the development of this peculiar neoplasm.

Trichoblastic neoplasm with apocrine differentiation

Trichoblastoma is a benign neoplasm with primitive hair follicle differentiation. The tumor is characterized by nests and cords of epithelial cells in an organized relation to stroma. The epithelial cells differentiate toward follicular germ and follicular sheath. More divergent differentiation in the form of sebaceous elements in trichoblastoma has infrequently been reported in the literature. We report a trichoblastic neoplasm showing typical features of trichoblastoma as well as areas of apocrine differentiation. The neoplasm, which was present for several months, was removed from the chin of a 31-year-old woman. Histologic examination showed a neoplasm composed of basaloid nests with occasional papillary mesenchymal bodies as well as ducts and glands exhibiting apocrine differentiation. Trichoblastoma with apocrine features is rarely reported in the literature.

Sebaceous carcinoma with apocrine differentiation

A 54-year-old male had a dome-shaped and skin-colored nodule on his nose. Histopathologically, we diagnosed this neoplasm as a low-grade sebaceous carcinoma rather than a sebaceoma based on the scanning magnification and cytology. This low-grade sebaceous carcinoma was associated with glandular structures. We regarded the glandular structures as those of apocrine glandular differentiation based on 1) the histopathologic features of the glandular structures formed by columnar luminal cells with evidence of decapitation secretion; 2) the expression of cytokeratin (CK) 19, CK8, CK8/18, and CK7 in the luminal cells; 3) the positive reaction of carcinoembryonic antigen and epithelial membrane antigen on the luminal surface and in the cytoplasm of the luminal cells; and 4) the common embryologic origin of the folliculosebaceous-apocrine unit. We found CK15 expression in undifferentiated cells within the mantles of normal hair follicles, suggesting that sebaceous stem cells might exist in mantles as follicular stem cells exist in bulge areas. Pluripotent stem cells in the folliculosebaceous-apocrine unit can give rise to follicular stem cells, sebaceous stem cells, and apocrine stem cells. Our patient's neoplasm showed apocrine glandular differentiation and partial immunohistochemical positivity for CK15 in the neoplastic aggregations. We believe this neoplasm originated from pluripotent stem cells destined to become sebaceous stem cells or from sebaceous stem cells, which also have the ability to differentiate within apocrine glands.

Trichoblastoma and sebaceoma in nevus sebaceus

We report two cases of an unusual combined adnexal neoplasm arising in a nevus sebaceus (NS). Clinically, both neoplasms presented in two women (46 and 78 years) as single, partially ulcerated nodules within NS situated on the scalp. Histopathologically, each neoplasm showed distinctive aggregations of basaloid cells with features of trichoblastoma adjacent to aggregations of neoplastic cells exhibiting features of sebaceoma. In both cases, typical features of NS were present. To the best of our knowledge, this unusual combined adnexal neoplasm comprised of trichoblastoma and sebaceoma could not be assigned to any previously described histopathologic entity. This "complex" adnexal neoplasm should be distinguished histopathologically from basal cell carcinoma with sebaceous differentiation and trichoblastoma with sebaceous differentiation.

Ectopic breast tissue and breast-like sweat gland metaplasias: an overlapping spectrum of lesions

There are many similarities in the morphology of benign and malignant lesions of the sweat glands and the breasts. The recently described cutaneous mammary-like sweat glands, also known as mixed sweat glands or apoeccrine glands, are also a likely source of selected proliferations that closely mimic those of the breast. We present three cases of breast-like lesions arising in the skin that demonstrate the ways in which the morphologic and pathologic continuum of the mammary glands, cutaneous mammary-like glands, and sweat glands can produce difficulties in precise diagnosis. The examples demonstrate that an anatomic location outside the milk line does not preclude the diagnosis of ectopic mammary tissue, and that lesions closely resembling those of the breast may also arise outside the milk line from conventional sweat glands or mixed sweat glands. The concept of homologous lesions of the breast, breast-like glands and sweat glands, in which morphology is partially mirrored by biochemical similarities, provides a perspective for classification of problematic cases of breast-like cutaneous lesions.