Monoclonal antibody MAT-1 against human tyrosinase can detect melanogenic cells on formalin-fixed paraffin-embedded sections

Evaluation of micrometastases in sentinel lymph nodes of cutaneous melanoma: higher diagnostic accuracy with Melan-A and MART-1 compared with S-100 protein and HMB-45

Accurate diagnosis of micrometastases in sentinel lymph nodes of cutaneous melanoma is critical for proper clinical management. S-100 protein and HMB-45 are the traditional immunomarkers widely used for this purpose. However, the interpretation of micrometastases by these markers is difficult with significant reduction in the diagnostic accuracy. S-100 protein demonstrates immunoreactivity for other nonmelanoma cells and obscures nuclear details, which are crucial for the interpretation of single cell metastases. We compared the new melanoma markers, Melan-A (clone A103) and MART-1 (clone M2-7C10), with S-100 protein and HMB-45, by examining 77 formalin-fixed paraffin-embedded sections of sentinel lymph nodes from 13 cases of primary cutaneous melanoma. CD68 (PG-M1) and hematoxylin-eosin-stained sections were also studied. Four pathologists interpreted the staining pattern after concealing the identity of each immunomarker. Az values (area under receiver operating characteristic curve) with receiver operating characteristic curve were higher with Melan-A (0.9742) and MART-1 (0.9779) compared with S-100 protein (0.8034) and HMB-45 (0.8651), demonstrating a higher diagnostic accuracy with Melan-A and MART-1 with superior detection of melanoma micrometastases. Melan-A and MART-1 showed sharp cytoplasmic immunoreactivity, almost exclusively restricted to the melanoma cells. Therefore, Melan-A and MART-1 are recommended for the evaluation of micrometastases in sentinel lymph nodes of cutaneous melanoma as a routine alternative to S-100 protein and HMB-45.

A panel immunoblot using co-incubated monoclonal antibodies for identification of melanoma cells

Antigen expression in melanoma is heterogeneous. Immunophenotyping using a panel of monoclonal antibodies may facilitate immunotherapy. An immunoblot procedure was developed to detect antigens in melanoma cells. Numerous monoclonal antibodies were tested to determine if (1) antigens were detected after transfer to membranes, (2) single bands or discrete multiple bands were obtained, (3) co-incubation of multiple monoclonal antibodies had no interference, and (4) banding patterns were non-overlapping. Antigens were selected based upon their association with melanoma and the availability of respective monoclonal antibodies. Antigens were melanoma antigen recognized by T-cells (MART-1), tyrosinase, tyrosinase-related protein 1 (TRP-1), S100, vimentin, glycoprotein 130 (gp130), a carcinoembryonic antigen (CEA)-like marker, KBA-62 and NKI-C3. Actin positive controls could be assessed simultaneously. Test samples were separated by polyacrylamide gel electrophoresis in a 4-15% polyacrylamide gradient, transferred to polyvinylidine fluoride membrane, blotted using a Fast-Blot apparatus (Pierce), and developed using diaminobenzidine/metal. Melanoma cell lines were immunophenotyped using this panel immunoblot, and were compared to a standard control and to non-melanoma cells. Up to four antigens could be detected simultaneously in a single lane of the immunoblot, using a single test sample of greater than 100000 cells.

Microphthalmia transcription factor in the immunohistochemical diagnosis of metastatic melanoma: comparison with four other melanoma markers

The diagnosis of metastatic malignant melanoma (MMM) may be difficult in surgical pathology, often complicated by the unpredictable spread of this tumor and its great variability on histologic evaluation. Traditionally used immunohistochemical markers on melanomas are insufficient because of either a relative lack of specificity (S100 protein) or variably reported sensitivity (HMB45). Information about some newer markers, such as tyrosinase (TYR) and Melan A, is more limited. Recently, based on the study of a small number of tumors, it was suggested that microphthalmia transcription factor (MITF) is 100% sensitive in the identification of metastatic melanoma. In the current study, we compared the diagnostic usefulness of MITF with that of four other markers in 266 cases of conventional metastatic melanomas from different sites, 33 cases of desmoplastic melanomas, and 1 case of melanoma with rhabdoid features. The specificity of MITF was evaluated by using a representative sample of control tumors. Microphthalmia transcription factor with nuclear positivity was seen in 235 of 266 cases of conventional MMM (88%), usually in more than 30% of tumor cells. However, some melanomas had only foci of MITF- and TYR-positive cells, whereas the majority of cells were generally S100 protein-positive. Only 1 of 30 desmoplastic melanomas (3%) had MITF-positive cells, representing epithelioid foci resembling conventional melanoma. Two cases had TYR in a similar pattern; all were HMB45-negative. One metastatic melanoma with rhabdoid features was negative for MITF and other markers except the S100 protein. Half of the S100 protein negative conventional melanomas (6 of 12) were MITF-positive, whereas 4 of 20 (20%) TYR-negative tumors had reactivity for MITF. The percentages of positive cases of MMM (10% or more tumor cells positive) diagnosed with the four other markers in descending order were 90% (S100 protein and TYR), 78% (melan-A), and 66% (HMB45). Microphthalmia transcription factor appeared to be specific, because significant reactivity was not found in 112 carcinomas, 20 lymphomas, 20 angiosarcomas, 20 fibrous histiocytomas, and 20 malignant peripheral nerve sheath tumors. However, positive nuclei were found focally among reactive histiocytes, especially in osteoclasts, epithelioid histiocytes, and sporadic other histiocytes. Microphthalmia transcription factor may be a valuable addition to the marker panel used in diagnosing melanoma, in combination with S100, TYR, and the other markers, but it is not present in cases of desmoplastic melanomas.

Immunohistochemical study of microphthalmia transcription factor and tyrosinase in angiomyolipoma of the kidney, renal cell carcinoma, and renal and retroperitoneal sarcomas: comparative evaluation with traditional diagnostic markers

Angiomyolipoma has a unique immunophenotype with co-expression of muscle-specific actin and melanocytic markers such as HMB-45 and Melan-A. The most recently developed melanocytic markers, microphthalmia transcription factor and tyrosinase, have not been studied in the diagnosis of angiomyolipoma. We tested 29 renal angiomyolipomas (21 classic histology, 4 epithelioid variants, 2 lipomatous variants, and 2 leiomyomatous variants) with an immunohistochemical panel, including microphthalmia transcription factor, tyrosinase, HMB-45, Melan-A, and muscle-specific actin. Results were compared with 15 renal cell carcinomas (9 conventional types, 6 with sarcomatoid change), 2 leiomyosarcomas, 5 liposarcomas, and 1 unclassified high-grade sarcoma. Microphthalmia transcription factor expression was seen in 22 of 29 angiomyolipomas, one renal cell carcinoma, and one well-differentiated liposarcoma (that is, 2 of 23 non-angiomyolipomas; sensitivity 75%, specificity 91%). Tyrosinase expression was seen in 4 of 29 angiomyolipomas and 0 of 23 non-angiomyolipomas (sensitivity 14%, specificity 100%). HMB-45 was positive in 24 of 29 angiomyolipomas and 0 of 23 non-angiomyolipomas (sensitivity 83%, specificity 100%). Melan-A was expressed by 25 of 29 angiomyolipomas and 0 of 23 non-angiomyolipomas (sensitivity 86%, specificity 100%). Muscle-specific actin was expressed by 29 of 29 angiomyolipomas and 2 of 23 non-angiomyolipomas (both leiomyosarcomas; sensitivity 100%, specificity 91% [100% excluding leiomyosarcomas]). Microphthalmia transcription factor showed the most widespread staining in angiomyolipoma (50% of cases staining more than half of the tumor cells) followed by Melan-A (24% of cases staining more than 50%). Only three cases showed positivity for all four melanocytic markers, while in one case each only microphthalmia transcription factor and Melan-A were positive. We conclude that microphthalmia transcription factor, but not tyrosinase immunostaining, has a sensitivity and specificity that rivals those of the established markers, HMB-45 and Melan-A, in the diagnosis of angiomyolipoma. Our data supports the use of a panel in difficult cases that includes antibodies to microphthalmia transcription factor, either Melan-A or HMB-45, and muscle-specific actin to provide the best mix of high sensitivity, high specificity, nuclear and cytoplasmic immunolocalization, and widespread staining of cells within a given tumor.

Retrospective study of 338 canine oral melanomas with clinical, histologic, and immunohistochemical review of 129 cases

Diagnostic records from 338 canine oral melanomas in 338 dogs received at the Veterinary Medical Diagnostic Laboratory (1992-1999) were reviewed. Of these tumors, 122 plus an additional 7 metastatic melanomas of unknown origin were selected for clinical follow-up, histologic review, and immunohistochemistry. Chow Chow, Golden Retriever, and Pekingese/Poodle mix breeds were overrepresented, whereas Boxer and German Shepherd breeds were underrepresented. There was no gender predisposition and the average age at presentation was 11.4 years. Forty-nine dogs were euthanized due to recurrence or metastasis. The average postsurgical survival time was 173 days. The gingiva and the labial mucosa were the most common sites. Most tumors were composed of either polygonal cells (27 cases, 20.9%), spindle cells (44 cases, 34.1%), or a mixture of the two (polygonal and spindle) (54 cases, 41.9%). Clear cell (3 cases, 2.3%) and adenoid/papillary (1 case, 0.8%) patterns were uncommon. The metastases of 6/6 oral melanomas had morphologic and immunohistochemical features similar to those of the primary tumors. Immunohistochemically, Melan A was detected in 113/122 oral (92.6%) and 5/7 (71.9%) metastatic melanomas. Only 4/163 nonmelanocytic tumors were focally and weakly positive for Melan A. Antibodies against vimentin, S100 protein, and neuron-specific enolase stained 129 (100%), 98 (76%), and 115 (89.1%) of 129 melanomas, respectively. Antibodies against other melanocytic-associated antigens (tyrosinase, glycoprotein 100) did not yield adequate staining. We conclude that Melan A is a specific and sensitive marker for canine melanomas.

Tyrosinase immunoreactivity in fine-needle aspiration samples of metastatic malignant melanoma

BACKGROUND

Tyrosinase, the rate-limiting enzyme in melanin synthesis, is a melanoma associated antigen that is recognized by both CD4+ and CD8+ T-cells in an HLA-restricted fashion. Peptides derived from the tyrosinase antigen currently are being utilized as a target for T-cells in several immunotherapy protocols for metastatic malignant melanoma (MMM) at the National Institutes of Health/National Cancer Institute. Serial fine-needle aspirations of metastatic lesions are performed to monitor the antigen expression of tyrosinase during treatment by immunostaining cytologic preparations with the monoclonal antibody T311.

METHODS

In the current study, 62 samples of MMM were evaluated for tyrosinase immunoreactivity on air-dried, acetone fixed cytospins and the corresponding formalin fixed, paraffin embedded cell block using an avidin-biotin immunoperoxidase method.

RESULTS

Positive immunoreactivity revealed a granular cytoplasmic staining in melanocytic cells. The current study results showed that 92% of samples (57 of 62) were T311 immunoreactive on cell block preparations, whereas only 61% (38 of 62) were immunoreactive on cytospin preparations. In 66% of samples (41 of 62) immunoreactivity for T311 was greater in the cell block sample than in the corresponding cytospin, whereas in only 3% of samples (2 of 62) was it greater in the cytospins. In 31% of samples (19 of 62) there was no significant difference in immunoreactivity between the 2 sample types.

CONCLUSIONS

The results of the current study show that tyrosinase is a sensitive marker for the detection of MMM; however, the optimal method of sample preparation for immunoperoxidase staining appears to be formalin fixation and paraffin embedding as tyrosinase immunoreactivity is diminished significantly in air-dried cytospin samples despite subsequent acetone fixation. Cancer (Cancer Cytopathol)

T311--an anti-tyrosinase monoclonal antibody for the detection of melanocytic lesions in paraffin embedded tissues

Tyrosinase is a key enzyme in melanin biosynthesis and represents a marker of melanocytic differentiation. We previously generated T311, a murine monoclonal antibody to the tyrosinase recombinant protein. This study was performed to evaluate T311 as a diagnostic immunohistochemical reagent for use on formalin-fixed paraffin-embedded pathological material. We analyzed the specificity of the antibody on a panel of normal and neoplastic tissues, and we assessed its sensitivity in a large number of metastatic and primary malignant melanomas, nevi, three angiomyolipomas, and two vitiligo specimens. T311 revealed intense reactivity on paraffin-embedded material. Immunoreactivity was limited to cells of melanocytic differentiation and no immunostaining was present in unrelated normal tissues and tumors. Eighty-four percent of metastatic malignant melanomas were immunoreactive with T311 and showed predominantly a homogeneous expression pattern. However, in primary melanomas of the desmoplastic/spindle cell type, T311 revealed a poor immunoreactivity. Nevi showed intense staining at the junctional zone, while the dermal component revealed decreasing reactivity towards deeper areas. Only one angiomyolipoma was focally immunoreactive with T311. Vitiligo specimens were immunonegative. We conclude that T311 is a specific and sensitive marker for the detection of melanocytic lesions in formalin-fixed paraffin-embedded tissues and a useful serological reagent for diagnostic pathology.

gp100 mRNA is more sensitive than tyrosinase mRNA for RT-PCR amplification to detect circulating melanoma cells in peripheral blood of melanoma patients

Two different melanocyte-specific mRNAs are studied as markers for circulating melanoma cells in vitro using the human melanoma cell line G361 and in vivo using blood samples from Japanese melanoma patients at different clinical stages. These mRNAs encode tyrosinase, the most essential enzyme for melanin synthesis, and gp100, a melanosomal matrix glycoprotein recognized by monoclonal antibody HMB-45. We used reverse-transcription polymerase chain reaction (RT-PCR) to detect tyrosinase mRNA and gp100 mRNA in peripheral blood. Since melanocytes would not normally be present in peripheral blood, the detection of those transcripts should indicate the presence of circulating melanoma cells. RT-PCR detection of these two mRNAs was highly sensitive and specific. Our in vitro study showed that as few as 10 melanoma cells in 0.125 ml normal blood could be detected. In in vivo study, 130 blood samples from 55 melanoma patients gave positive and variably sensitive results, whereas no samples from healthy controls or patients with other cancers gave positive results. Tyrosinase mRNA was not detected in any of the melanoma patients. gp100 mRNA was detected in 12 of 55 melanoma patients, in none of five stage I patients (0%), in four of 26 stage II patients (15.4%), in one of six stage III patients (16. 7%) and in seven of 18 stage IV patients (38.9%). Thus gp100 mRNA is a more sensitive marker for detecting circulating melanoma cells compared with tyrosinase mRNA.

Tyrosinase immunoreactivity in formalin-fixed, paraffin-embedded primary and metastatic melanoma: frequency and distribution

Monoclonal antibody T311 specifically detects tyrosinase protein expression. Tyrosinase-derived peptides are recognized by CD8+ T-cells and applied in immunotherapy. We examined formalin-fixed paraffin-embedded tissue of 50 melanoma (primary n=31, metastatic n=19) and 41 control cases (junctional, dermal, compound, Spitz, Reed, balloon-cell nevi) by immunochemistry using the alkaline phosphatase-anti-alkaline phosphatase method after antigen retrieval. Staining with mAb T311 showed a sensitivity of 94% for melanoma with a very high specificity for melanocytic cells. Immunopositivity (94% of melanomas overall) correlated inversely with clinical stage: clinical stage I and stage II showed 100%, stage III and stage IV 86% immunoreactivity each. Staining changed from an exclusively homogeneous pattern in early stages to a more heterogeneous pattern in later stages. Melanocytic control tissue like nevi of different subtypes all showed weak to moderate, homogeneous immunoreactivity with polarity towards the epidermis. RT-PCR ELISA analysis of short-term melanoma cell cultures displayed mRNA expression in only half of the originally immunopositive tumors only, suggesting rapid mRNA expression loss in culture. mAb T311 allows detection of melanoma-associated tyrosinase protein expression and thus profiling of melanomas using routine archival tissue suited for immunotherapy approaches involving tyrosinase derived epitopes.