Retroperitoneal lymphangioleiomyomatosis associated with endosalpingiosis

A case of retroperitoneal lymphangioleiomyomatosis (LAM) arising from endosalpingiosis is described. A 25-year-old woman with no history of tuberous sclerosis or hormonal therapy presented with a painless, palpable abdominal mass. Computed tomographic and magnetic resonance imaging studies of the abdomen demonstrated a 4 cm cystic mass in the retroperitoneum. Macroscopically, the excised retroperitoneal cyst was multilocular and measured 4.0 x 3.5 x 3.5 cm. Histologically, the lesion demonstrated three components. The first comprised multiple cysts or glands lined by columnar epithelial cells with cilia. The second component was a condensation of small stromal cells immediately subjacent to the cystic epithelium or glands. The third component was a thick exterior wall composed of plump spindle cells with clear to palely eosinophilic cytoplasm in a fascicular pattern, and slit-like vascular spaces, resembling LAM. Immunohistochemically, the epithelium and glands were positive for cytokeratin 7. The stromal cells were positive for vimentin and CD10. The cells of the LMA-like component showed positive staining for HMB45, alpha-smooth muscle actin, muscle actin and h-caldesmon. The lesion, LAM arising from endosalpingiosis, represents a distinctive pathologic entity that should be recognized and studied further. This type of lesion should be included in the differential diagnosis of retroperitoneal cystic lesions.     

Cystic pulmonary metastases of endometrial stromal sarcoma of the uterus, mimicking lymphangiomyomatosis: A case report with immunohistochemistry of HMB45

A case of endometrial stromal sarcoma (ESS) showed cystic pulmonary metastases mimicking lymphangiomyomatosis (LAM). A 58-year-old female, who had undergone total hysterectomy for low-grade ESS 16 years previously, had repeated bouts of pneumothorax. Multiple then-walled cysts in the perlpheral lung were revealed by radiological examinations. In an open-lung blopsy specimen, cystlc lesions were surrounded by layers of spindle-shaped cells of varying thickness that resembled LAM. However, In addltion to subtle histological differences from LAM, HMB45 (antimelanoma antibody) showed positive In LAM (n=3), but was negative in ESS (M) and the cystlc leslons of this case. Using myogenic markers (desmin and α-smooth muscle actin), metastatlc ESS could be immunohistochemically differentiated from mesenchymal cystlc hamartoma (n=1). HMB45 Immunohistochemistry is useful in the differential diagnosis of cystic puimonary lesions.     

Role for activation of matrix metalloproteinases in the pathogenesis of pulmonary lymphangioleiomyomatosis

BACKGROUND: Matrix metalloproteinases (MMPs) have been shown to be involved in the pathogenesis of the destructive pulmonary lesions in patients with lymphangioleiomyomatosis (LAM); in the present report, the activation of these enzymes is examined. OBJECTIVE: To evaluate the role of MMPs and their activating enzymes, immunohistochemical and confocalmicroscopic techniques were used to localize alpha-smooth muscle actin (alpha-SMA), HMB-45, proliferating cell nuclear antigen (PCNA), MMP-2, membrane-type 1 MMP (MT1-MMP), MT2-MMP, and MT3-MMP in lung tissues from 10 women with LAM. Tissue samples were obtained from 5 patients before treatment and in 5 patients after hormone treatment (progesterone and/or tamoxifen citrate). RESULTS: Staining for alpha-SMA and MMP-2 was present in all the abnormal smooth muscle cells (LAM cells) in both groups. The percentages of PCNA-, MMP-2-, or MT1-MMP-positive LAM cells were much higher in the untreated group than in the treated group, whereas the percentages of HMB-45-reactive LAM cells were similar in both groups. The reactions for MT1-MMP and PCNA were preferentially localized in small spindle-shaped LAM cells; the reaction for HMB-45 was found in large epithelioid LAM cells. Many of the PCNA-positive cells were also positive for MT1-MMP. Staining for MT2-MMP and MT3-MMP was negative. CONCLUSIONS: This study demonstrates an association between cellular proliferation and the presence of MT1-MMP in LAM cells. The activation of MMP-2 by MT1-MMP may play an important role in the destruction of lung tissue in this disorder.     

Extrapulmonary lymphangioleiomyomatosis (LAM): clinicopathologic features in 22 cases

We describe the lesions of extrapulmonary lymphangioleiomyomatosis (LAM) affecting the lymph nodes of the mediastinum and retroperitoneum in 22 women (mean age +/- SD, 42.4+/-10.5 years). In most of these patients, the diagnosis of extrapulmonary LAM preceded that of pulmonary LAM, usually by 1 to 2 years. Eleven patients had distinct symptoms, including chylous pleural effusion and/or ascites, abdominal pain, and palpable abdominal masses. In the other 11 patients, the masses caused no symptoms. Well-circumscribed, encapsulated masses, measuring up to 20 cm in size, occurred in the mediastinum in 2 patients, the upper retroperitoneum in 15, extensive areas of the retroperitoneum in 2, and the pelvis in 3. The masses exceeding 3 cm in diameter contained large, multiple cysts filled with yellow-tan chylous fluid. Histologically, the masses were characterized by a proliferation of smooth muscle cells (LAM cells) arranged in fascicular, trabecular, and papillary patterns, which were associated with slit-like vascular channels. The LAM cells varied from small, spindle-shaped cells to large epithelioid cells. Immunohistochemical studies showed a strong reactivity of most LAM cells for alpha-smooth muscle actin and smooth muscle myosin heavy chain and a weak to moderate reactivity of a lesser number of cells for desmin and nonmuscle myosin heavy chain II-B. A reaction for HMB-45 and estrogen and progesterone receptors was observed mainly in epithelioid LAM cells. These patterns of reactivity are similar to those observed in pulmonary LAM. However, the chylous cysts are not a feature of pulmonary LAM and are thought to result from obstruction of lymphatics.     

Clear-cell proliferation of the lung with lymphangioleiomyomatosis-like change

AIMS: To describe two cases of a peculiar pulmonary lesion, which expand both the morphological and the immunophenotypic spectrum of perivascular epithelioid cell (PEC)-related disorders. METHODS AND RESULTS: One man and one female, with and without the tuberous sclerosis complex (TSC), respectively, showed pulmonary cysts and small nodules on computed tomography scan. In the former, lymphangioleiomyomatosis (LAM) was suspected. In both cases, an open lung biopsy was performed, whose cut surface displayed numerous cysts lined by thin/thick septa. Microscopically, the septa were associated with micronodular or interstitial proliferation of medium/large-sized elements with abundant clear (periodic acid-Schiff-positive/diastase-sensitive) cytoplasm and distinct cell borders, embedded in fibrous tissue. The elements were CD34+, vimentin-positive and, to a lesser extent, HMB-45+ and MART-1+. The stains for specific muscle actin, desmin, S100 protein, CD31, FVIIIRAg, cytokeratins, CD45, CD68, oestrogen and progesterone receptors were all negative. Ki67 labelling was <1%. Electron microscopy displayed cytoplasmic vacuoles containing glycogen particles. The TSC1 and TSC2 gene status could not be assessed because of poor DNA preservation. In the man with TSC, a focus of micronodular pneumocyte hyperplasia was also found. CONCLUSIONS: Because of the coexpression of CD34 and melanoma-associated antigens and the occurrence of TSC in one patient, the cases described here add a new piece to the puzzle of PEC lesions and contribute to the open discussion on the origin of LAM and LAM-like proliferations.     

Adenoleiomyomatous hamartoma of the lung]

The author described an adenoleiomyomatous hamartoma of the lung. The hamartoma was well circumscribed and measured 2.5 x 3.0 x 3.0 cm. This type of hamartoma is a rare lesion in literature described only in single cases, and without performed immunohistochemistry. In our case, the hamartoma was formed by slit or irregular glandular-like spaces lined by cuboid or columnar epithelial cells. Located around these spaces, fascicles and bundles of smooth muscle tissue with a positive antibody reaction to desmin, smooth muscle actin, and calponin, were found. Reaction with CD34 and S100 protein antibodies was negative. In the discussion, the author draws attention to disunity of terms and nomenclature of similar lesions. After three years of post-operative clinical follow-up, the patient is asymptomatic and without any signs of lung disorder.     

D2-40 labeling in lymphangiomyoma/lymphangiomyomatosis of the soft tissue: further evidence of lymphangiogenic tumor histogenesis

We examined ten cases of extrapulmonary lymphangioleiomyoma/lymphangioleiomyomatosis (LAM; all patients female; median age 46.5 years) for immunohistochemical labeling with a monoclonal antibody against podoplanin (D2-40), which is specific for lymphatic endothelial lining. We found positive staining in thin-wall branching vessels reflecting the lymphatic nature of tumor vessels in all cases tested. In contrast, perivascular (HMB-45 positive) myoid cells were not detected by D2-40. The D2-40 labeling confirms the current concept of lymphangiogenic origin of the tumor vessels in LAM. In addition, this study makes a further contribution to the immunohistochemical mapping of this antibody in vascular tumors. Finally, the use of this commercially available antibody provides an additional help in the differential diagnosis of LAM from other soft tissue tumors.     

Angiomyolipoma with epithelial cysts of the kidney in a man

Angiomyolipoma (AML) is a well-characterized tumor composed of vascular, smooth muscle and adipose elements. Recently, AML with epithelial cysts (AMLEC) has been described as a cystic variant of AML. Herein is reported an AMLEC in a 55-year-old man, and to the authors' knowledge this is the first case report of AMLEC in Japan. He was referred to hospital because of microhematuria. A left renal tumor was noted and partial nephrectomy was performed. Histology indicated that the tumor was composed of epithelial cysts, compact subepithelial stroma and muscle-predominant AML. Immunohistochemically, the subepithelial compact stroma and muscle-predominant AML were positive for HMB-45, estrogen receptor (ER), progesterone receptor (PR), CD10, smooth-muscle actin and desmin. Epithelial cysts were positive for pancytokeratin but negative for HMB-45, ER and PR. This tumor was diagnosed as AMLEC, mainly based on the immunohistochemical result that subepithelial compact stroma and muscle-predominant AML were positive for HMB-45. The patient was alive with no evidence of recurrence at 2 years postoperatively. This case was very interesting because it suggests that AMLEC should enter into the differential diagnosis of adult renal neoplasms.     

Renal angiomyolipoma with epithelial cysts: a rare entity and review of literature

Renal angiomyolipoma (AML) with epithelial cysts (AMLEC) is a comparatively rare benign renal tumor that is recently recognized as a distinct entity and there are relatively few reported cases in the English-language literature. To date 19 cases of AMLEC have been reported in 2 case series and a few case reports. AMLEC has been described as a cystic variant of AML. Herein we reported an AMLEC in a 25-year-old female patient, and to the best of our knowledge this is the first case report of AMLEC in Chinese. She was incidentally found to have a kidney-occupying lesion during a routine medical examination for 1 month. CT examination demonstrated a multilocular cystic lesions arising from right-kidney lower pole. The patient underwent the partial nephrectomy. Histological examination of the tumor was composed of epithelial cysts, compact subepithelial mullerian-like stroma and muscle-predominant AML. Immunohistochemically, epithelial cysts were positive for CK but negative for ER, PR, CD10 and HMB-45; the subepithelial stroma and muscle-predominant AML were positive for ER, PR and HMB-45; the subepithelial stroma was negative for SMA, but muscle-predominant AML was positive for SMA. The final histopathological diagnosis was AMLEC.     

Palisaded encapsulated neuroma: an immunohistochemical study

Ten palisaded neuromas of the skin were studied immunohistochemically for the presence of S-100 protein, epithelial membrane antigen, neurofilaments, glial fibrillary acidic protein, and positivity with the Leu-7 monoclonal antibody. In all cases, the fascicles of tumor cells were positive for S-100 protein and negative for epithelial membrane antigen; the tumor capsules were negative for the former in all cases but positive for the latter in seven of ten cases. In three lesions, epithelial membrane antigen-positive cells formed sheaths around fascicles of tumor cells. Axons were demonstrated by anti-neurofilament antibody in seven lesions. None of the lesions stained for glial fibrillary acidic protein. All of them showed positivity with the Leu-7 antibody, which stained both tumor spindle cells as well as membranous profiles consistent with myelin sheaths. These results indicate that the tumor is composed of cells of schwannian differentiation whereas the capsule and sheaths surrounding intratumoral fascicles are of perineurial origin. They also indicate the presence of axons, some of which are myelinated. Our findings support the concept of a close relationship between palisaded and traumatic neuroma.     

Localized retroperitoneal lymphangioleiomyomatosis mimicking malignancy. A case report and review of the literature

Lymphangioleiomyomatosis (lymphangiomyomatosis [LAM]), a rare disease of unknown etiology that is seen only in women usually in the reproductive period, generally presents with features of pulmonary involvement. Extrapulmonary involvement, such as angiomyolipomas and retroperitoneal adenopathy, can occur in up to 75% of cases. It is very rare, however, for patients to present with features of extrapulmonary LAM. We present an unusual, localized case of LAM presenting with neurologic symptoms related to a retroperitoneal mass in a 51-year-old woman. Magnetic resonance imaging showed that the mass involved retroperitoneal lymph nodes, and a clinical diagnosis of atypical sarcoma (possibly from a uterine primary) was made. The mass was resected, and a total abdominal hysterectomy was performed. On pathologic examination, the mass showed classic histologic features of LAM with spread along lymphatic channels in the lymph nodes. Intralymphatic projections simulated lymphatic metastasis; however, the cytologic features were benign. Immunostains revealed the tumor to be positive for smooth muscle actin and desmin, but negative for HMB-45. The uterus was unremarkable, except for a subserosal leiomyoma. Although intratumoral variability for HMB-45 has recently been described, to the best of our knowledge, this is the first documented case of HMB-45-negative, histologically classic LAM. Because of the presence of several atypical features in this case, such as age, location, compressive neurologic presentation, radiologic impression of atypical sarcoma, and HMB-45 negativity, we feel that this case may represent a distinct, as yet uncharacterized variant of LAM.     

Renal angiomyolipoma: further immunophenotypic characterization of an expanding morphologic spectrum

BACKGROUND: Renal angiomyolipoma is a benign tumor histologically characterized by proliferation of spindle cells, epithelioid cells, and adipocytic cells in concert with many thick-walled blood vessels. To add further diagnostic confusion, an epithelioid cell-predominant variant of renal angiomyolipoma has recently been described. HMB-45 immunoreactivity correlates with ultrastructural striated organelles that closely resemble premelanosomes, although no evidence of melanogenesis has been documented in this tumor. OBJECTIVE: To further characterize the immunophenotypic and ultrastructural profile of renal angiomyolipoma based on phenotypic cell type (epithelioid, spindle, and adipocytic cell). DESIGN: Formalin-fixed, paraffin-embedded tissues from 27 renal angiomyolipomas and 8 renal cell carcinomas were immunostained with monoclonal antibodies to the melanoma-associated antigens HMB-45, HMB-50, NKI/C3 (CD63), and tyrosinase; the smooth muscle-related antigens calponin and muscle-specific actin (HHF-35); S100; and cytokeratin (CK). All renal angiomyolipomas were also immunostained with a polyclonal antibody to renin. Ultrastructural examination was performed on 9 selected cases. RESULTS: All renal angiomyolipomas stained positive for HMB-45, HMB-50, NKI/C3, muscle-specific actin (HHF-35), and calponin. Overall, HMB-45, HMB-50, and NKI/C3 preferentially stained the epithelioid cells. Tyrosinase staining was present in 50% of the renal angiomyolipomas with adequate tissue for staining (12 of 24 cases); positive staining and intensity paralleled HMB-45, HMB-50, and NKI/C3. Muscle-specific actin (HHF-35) and calponin preferentially stained the spindle cells. The adipocytic cells stained positive for both melanoma-associated antigens and smooth muscle antigens. Epithelioid cells, spindle cells, and adipocytic cells were CK, S100, and renin negative. Ultrastructural findings paralleled immunohistochemical staining patterns. Premelanosome-like organelles and electron dense granules were more readily detected in the epithelioid cells within the tumor, whereas ultrastructural characteristics of smooth muscle cells were more easily found in the spindle cells. All renal cell carcinomas stained positive for CK, NKI/C3 staining was variable, and all were negative for HMB-45, HMB-50, smooth muscle actin (HHF-35), and calponin. CONCLUSION: In renal angiomyolipoma, the epithelioid and spindle cells have preferential staining patterns for melanoma-associated antigens versus smooth muscle antigens, respectively. Positivity in renal angiomyolipoma for HMB-50, NKI/C3, and tyrosinase, in addition to HMB-45, provides evidence for the presence of different melanoma-associated gene products. Immunophenotypic overlap of the 3 histologically distinct renal angiomyolipoma cell populations suggests a common cell line, supporting a unitarian concept for renal angiomyolipoma. Ultrastructural characteristics of the 3 renal angiomyolipoma cell phenotypes parallel the immunophenotype, giving further support to a common cell line. Our study lends further credence to the perivascular epithelioid cell concept as proposed by Bonetti and colleagues.     

Lymphangiomyomatosis and angiomyolipoma: closely related entities characterized by hamartomatous proliferation of HMB-45-positive smooth muscle

Angiomyolipoma is a hamartomatous condition which can occur as a component of the tuberous sclerosis complex. Lymphangiomyomatosis, another hamartomatous lesion occurring predominantly in the lungs, has long been suspected to be related to angiomyolipoma and tuberous sclerosis because of occasional clinical associations. We undertook this study to provide further support for the close relationship between these two entities. Five cases of lymphangiomyomatosis and 20 case of angiomyolipoma were retrieved for histological review and immunohistochemical studies. The antibodies used were anti-muscle specific actin (HHF-35), anti-desmin (D33) and antimelanoma (HMB-45). Lesions featuring smooth muscle proliferation were used as controls. The proliferated smooth muscle cells in both lymphangiomyomatosis and angiomyolipoma were much plumper and paler or even clear, when compared with the deeply eosinophilic cytoplasm of the normal spindly smooth muscle cells and those of leiomyomas. Their nuclei were round to oval and pale rather than elongated and dark. Cells with bizarre nuclei were commoner in angiomyolipoma (18/20 cases) than lymphangiomyomatosis (1/5). In 12 cases of angiomyolipoma there were foci indistinguishable from lymphangiomyomatosis, i.e. plump spindle cells arranged in short fascicles around ramifying endothelium-lined spaces. All five cases of lymphangiomyomatosis stained for muscle-specific actin, desmin and HMB-45. For angiomyolipomas, the positivity rates for these markers were: 20/20, 17/20 and 18/20, respectively, including one case that was negative for both desmin and HMB-45. The various smooth muscle proliferations and tumours selected as controls were uniformly HMB-45 negative. The distinctive cytological features, morphological overlap and immunophenotypic profile all support a close relationship between lymphangiomyomatosis and angiomyolipoma, which probably represent different morphological manifestations of hamartomatous proliferation of a peculiar form of HMB-45-positive smooth muscle.     

Pathogenesis of multifocal micronodular pneumocyte hyperplasia and lymphangioleiomyomatosis in tuberous sclerosis and association with tuberous sclerosis genes TSC1 and TSC2

Tuberous sclerosis (TSC) is a rare, genetically determined disorder / familial tumor syndrome, currently diagnosed using specific clinical criteria proposed by Gomez, including the presence of multiorgan hamartomas. Pulmonary involvement in TSC is well known as pulmonary lymphangioleiomyomatosis (LAM), which has an incidence of 1-2.3% in TSC patients. LAM has immunohistochemical expression of both smooth-muscle actin and a monoclonal antibody specific for human melanoma, HMB-45. It has recently been reported that multifocal micronodular pneumocyte hyperplasia (MMPH) associated with TSC should be considered as a distinct type of lung lesion, whether it occurs with or without LAM. Two predisposing genes have been found in families affected by TSC; approximately half of the families show linkage to TSC1 at 9q34.3, and the other half show linkage to TSC2 at 16p13.3. TSC genes are considered to be tumor suppressor genes, and mutations in them may lead to abnormal differentiation and proliferation of cells. Tuberin, the TSC2 gene product, has recently been found to be expressed in LAM and MMPH. In this article we discuss the histogenesis and genetic abnormalities of neoplastic lesions associated with TSC, and we review the current understanding of the pathogenesis of pulmonary hamartomatous lesions such as LAM and MMPH in TSC.     

Immunohistochemical study of hepatic angiomyolipoma

An immunohistochemical study was performed on nine hepatic angiomyolipomas (AML) found in eight patients. Histologically, the tumors were fundamentally composed of the three heterogeneous tissue components of blood vessels, smooth muscle cells (SMC), and fat cells, although the proportions and distributions were quite variable from tumor to tumor and from area to area in the same tumor. Additionally, cellular pleomorphism and atypia with occasional bizarre giant cells were found in the SMC component. This histologic feature might lead to a mistaken diagnosis of malignant neoplasm, and pathologists should therefore be aware of the broad histologic spectrum of hepatic AML. However, the immunostaining patterns were basically the same in all nine tumors. All tumor components were negative for epithelial membrane antigen (EMA) and for cytokeratin. The spindle-shaped SMC component of the tumor was occasionally positive for vimentin, desmin and alpha-smooth muscle actin, whereas epithelioid SMC were negative for all three. Both the epithelioid and spindle-shaped SMC were occasionally positive for S-100 and neuron-specific enolase. All types of SMC in the tumor, whether spindle, epithelioid, intermediate or pleomorphic SMC, were strongly positive for HMB-45, a melanoma-specific monoclonal antibody. Fat cells were occasionally positive for S-100. Endothelial cells were positive for factor VIII-associated antigen. Among hepatic tumors HMB-45 reactivity is, so far as we know, found exclusively in the SMC of AML, and the HMB-45 reactivity of a hepatic tumor is thus clearly an important piece of information in the diagnosis of AML.     

Alveolar adenoma of the lung

Solitary coin lesions in the lung invoke an expanding differential diagnosis and while pulmonary hamartoma and a neuroendocrine tumour are the commonest causes, there are other lesions that need to be considered. Alveolar adenoma and sclerosing pneumocytoma are two such lesions.This is a case of an alveolar adenoma in a 41-year-old asymptomatic female who was found to have a peripheral solitary lesion on routine chest X-ray. In view of suspicious cytology, she had a left lower lobectomy. The lesion was well-circumscribed and composed of multiple cystic structures of varying size. The cysts were lined by epithelial cells ranging from flat to cuboidal to hobnail, and conformed to type II pneumocytes. The stroma between the cysts contained bland spindle shaped cells and mixed inflammation, including several mast cells. Immunohistochemistry showed the cyst lining cells to be positive for epithelial markers and TTF-1. The stromal cells were negative for these stains.Alveolar adenoma is a rare benign cystic neoplasm of lung with a superficial resemblance to a lymphangioma and is thought to arise from type II pneumocytes.     

Leiomyomatosis-like lymphangioleiomyomatosis of the colon in a female with tuberous sclerosis.

Smooth muscle lesions of the large bowel, excluding the rectum, are generally rare, and diffuse smooth muscle lesions, termed leiomyomatosis, are even rarer. In this report, we document, for the first time, leiomyomatosis-like lymphangioleiomyomatosis (LAM) of the ascending, transverse, and descending colon in association with bilateral renal angiomyolipoma (AML) in a 30-year-old Chinese female with tuberous sclerosis complex (TSC). She presented with protracted constipation for which a colectomy was performed. Histology disclosed multiple confluent nodular CD34 and CD117 negative smooth muscle proliferation within the large bowel wall, whereas the renal biopsy revealed typical features of AML. Interestingly, the epithelioid smooth muscle cells of both the colonic and renal lesions were HMB45 positive, suggesting that leiomyomatosis-like LAM of the colon, pulmonary LAM and AML are closely related entities. The patient remained free of complications for the last five years after surgery. Leiomyomatosis-like LAM of the large bowel probably represents another manifestation of the tendency of TSC to be associated with proliferative lesions.     

Diagnostic value of HMB-45 and anti-Melan A staining of sentinel lymph nodes with isolated positive cells.

Numerous immunohistochemical stains have been employed to detect metastatic melanoma in sentinel lymph node (SLN) biopsies. HMB-45 is considered by some as a specific tool to detect early metastatic melanoma (1). Occasionally, one or two isolated HMB-45-positive cells may cause complications in diagnostic interpretation. The goal of this study was to evaluate the reliability of HMB-45 staining of SLNs with sparse isolated positive cells and to compare its staining with anti-Melan A antibody. HMB-45 and anti-Melan A antibody immunostaining was performed on (Group A) 15 histologically negative SLNs excised from patients with malignant melanoma (MM) and on (Group B) 15 histologically negative SLNs excised from patients with breast carcinoma (BC). None of the patients had clinical evidence of systemic metastasis at the time of SLN biopsy. Five cutaneous biopsies with changes of postinflammatory hyperpigmentation (PIHP) were also stained with both antibodies. HMB-45 staining was repeated in all Group B SLNs after blocking endogenous biotins. Electron-microscopic studies were performed on all cases of PIHP. Isolated HMB-45-stained cells were present in 6 of 15 SLNs removed for MM; 8 of 15 for BC; and 3 of 5 cutaneous biopsies of PIHP. HMB-45 reactivity persisted after blocking endogenous biotins in 6 of 8 positive SLNs from Group B. Anti-Melan A antibody was negative in all SLNs of group A and B and in dermal melanophages of all five cases of PIHP. HMB-45 positivity was demonstrated in histologically negative SLNs and cutaneous biopsies, especially in the milieu of aggregated melanophages. Phagocytosis of premelanosomes by macrophages in the draining lymph nodes may account for isolated cell positivity and can hinder correct diagnostic interpretation. HMB-45 may not be a reliable marker for the detection of micro-metastasis of MM and requires correlation with other immunohistochemical markers, such as anti-Melan A antibody, to enhance specificity.