Micromorphometric features of positive sentinel lymph nodes predict involvement of nonsentinel nodes in patients with melanoma

The aim of the present study was to determine whether micromorphometric features of positive sentinel lymph nodes (SLNs) from patients with melanoma are useful for predicting further nodal involvement in completion lymph node dissection (CLND) specimens. Of 986 patients with melanoma undergoing SLN biopsy between March 1992 and February 2001, 175 (17.7%) had at least 1 positive SLN and 140 had subsequent CLND specimens available for review. Further nodal involvement in CLND specimens was present in 24 (17.1%) of 140 patients. Of 8 micromorphometric features of the SLNs that were assessed, the presence of metastases in CLND specimens was correlated significantly with a tumor penetrative depth (maximum distance of melanoma cells from the inner margin of the SLN capsule) of more than 2 mm (P < .05), a deposit size of more than 10 mm2 (P < .01), the presence of melanoma cells in perinodal lymphatic vessels (P < .01), and the effacement of nodal architecture by metastatic melanoma cells (P < .05). Our results indicate that some morphologic features of melanoma metastases in SLNs predict the likelihood of further nodal involvement in CLND specimens.     

Pathologic evaluation of sentinel lymph nodes in colorectal carcinoma

BACKGROUND: The identification of lymph node metastases in colorectal resection specimens is necessary for accurate tumor staging. However, routine lymph node dissection by the pathologist yields only a subset of nodes removed surgically and may not include those nodes most directly in the path of lymphatic drainage from the tumor. Intraoperative mapping of such sentinel lymph nodes (SLNs) has been reported in cases of melanoma and breast cancer. We applied a similar method to cases of colorectal carcinoma, with emphasis on the pathology of the SLNs. METHODS: Eighty-three consecutive patients with colorectal carcinoma were evaluated after intraoperative injection of 1 to 2 mL of 1% isosulfan blue dye (Lymphazurin) into the peritumoral subserosa. Blue-stained lymph nodes were suture-tagged by the surgeon within minutes of the injection for identification by the pathologist, and a standard resection was performed. Designated SLNs were sectioned at 10 levels through the block; a cytokeratin immunostain (AE1) was also obtained. To evaluate the possibility that increased detection of metastases in the SLN might be solely due to increased histologic sampling, all initially negative non-SLNs in the first 25 cases were sectioned also at 10 levels. RESULTS: Sentinel lymph nodes were identified intraoperatively in 82 (99%) of 83 patients and accounted for 152 (11.9%) of 1275 lymph nodes recovered, with an average of 1.9 SLNs per patient. A total of 99 positive lymph nodes (38 positive SLNs and 61 positive non-SLNs) were identified in 34 node-positive patients. The SLNs were the only site of metastasis in 17 patients (50%), while 14 patients (41%) had both positive SLNs and non-SLNs. Three patients (9%) had positive non-SLNs with negative SLNs, representing skip metastases. In patients with positive SLNs, 91 (19%) of 474 total lymph nodes and 53 (12%) of 436 non-SLNs were positive for metastasis. In patients with negative SLNs, 8 (1%) of 801 total lymph nodes and 8 (1.2%) of 687 non-SLNs were positive for metastasis. Multilevel sections of 330 initially negative non-SLNs in the first 25 patients yielded only 2 additional positive nodes (0. 6%). All patients with positive SLNs were correctly staged by a combination of 4 representative levels through the SLN(s) together with a single cytokeratin immunostain. CONCLUSIONS: Intraoperative mapping of SLNs in colorectal carcinoma identifies lymph nodes likely to contain metastases. Focused pathologic evaluation of the 1 to 4 SLNs so identified can improve the accuracy of pathologic staging.     

Melanocytic nevi simulant of melanoma with medicolegal relevance

A group of melanocytic benign nevi are prone to be misdiagnosed as nodular or superficial spreading melanoma. This review illustrates the most frequent forms of these nevi in direct comparison with their malignant morphologic counterparts. The nevi are: hyper-cellular form of common nevus to be distinguished from nevoid melanoma, Spitz nevus (vs spitzoid melanoma), Reed nevus (vs melanoma with features of Reed nevus), cellular atypical blue nevus (vs melanoma on blue nevus), acral nevus (vs acral melanoma), Clark dysplastic nevus (vs superficial spreading melanoma), desmoplastic nevi (vs desmoplastic melanoma), benign proliferative nodules in congenital nevi (vs melanoma on congenital nevi), epithelioid blue nevus (vs animal type melanoma) and regressed nevus (vs regressed melanoma). For each single ‘pair’ of morphological look-alikes, a specific set of morphological, immunohistochemical and genetic criteria is provided.     

Intralymphatic nevus cells in benign nevi

The histogenesis of nevus cell aggregates in lymph nodes lesion is controversial, and various hypotheses have been used to explain their origin. One of them is the transport of cells from cutaneous nevi or lesions to lymph nodes, called mechanical transport theory. We investigated in our cases of benign nevi to obtain evidence to substantiate this theory. A total of 369 benign cutaneous nevi were prospectively evaluated in excisional biopsy samples. Immunohistochemical stainings for CD31 and podoplanin (D2-40) were performed in the cases with intralymphatic nevus cell aggregate (ILNA), suspected for ILNA, and/or intralymphatic nevus cell protrusion. A total of 13 ILNAs were found in 10 patients. Six ILNA were verified with their histology as well as immunohistochemically with D2-40 and CD31. Protrusions of nevus cells inside the lymphatics (intralymphatic nevus cell protrusion) were seen in all cases of ILNA and also in 27 nevi where an ILNA was not observed. In most nevi, the perilymphatic orientation of nevus cells and their affinity to the lymphatics were observed. We suggested that ILNAs can be dislodged with local minor trauma and be carried inside the lymphatic vessel to the draining lymph node. Besides, whether ILNA or not, nevus cells could also move toward lymphatic spaces with mechanical effects due to their affinity to lymphatics and their localizations that are very close to the endothelium. Our findings might support the mechanical transport theory.     

Melanocytic nevi in children

Melanocytic nevi in children can be acquired or congenital. The vast majority are benign but diagnosis can be difficult. Nevi in newborns and nodular proliferations in giant congenital nevi can display histological features that lend to their misdiagnosis as melanoma. Acquired melanocytic nevi in children are often Spitz nevi or related nevi. These lesions are too often misdiagnosed as melanoma. On the other hand, clinicians and pathologists must be aware that melanoma does occur in childhood, albeit very rarely. It is exceptionally rare in prepubescent individuals. It can be associated with the following risk factors: giant congenital nevus, family history of melanoma, xeroderma pigmentosum, and immunosuppression. Melanoma in children younger than 10 years of age is extremely rare and has different clinical and histopathological features than those that arise in postpubescents, often being confused with a Spitz's nevus. Consequently, the diagnosis is often made too late. It should be emphasized that thickness is the main prognostic parameter in childhood melanoma and that early diagnosis is also crucial in this age group. The lesion must therefore be examined in a complete excision and not in a partial biopsy, and if atypical features are present it must be reviewed by an expert. On the other hand extreme caution should be exercised when diagnosing melanoma in children, as some benign lesions exhibit similar histologic features.     

The diagnostic utility of PRAME and p16 in distinguishing nodal nevi from nodal metastatic melanoma

The status of the sentinel lymph node is the strongest predictor of recurrence in patients with malignant melanoma, making accurate distinction between nodal metastases and nodal nevi of paramount importance. We explored the utility of p16 and PRAME in differentiating nodal nevi from metastatic melanoma by immunohistochemistry. We searched our institutional database for cases of nodal nevi and nodal metastatic melanoma. p16 and PRAME expression were assessed with immunolabeling quantified by extent of nuclear positivity (0−25 %, >25 %-50 %, >50 %-75 % and >75 %). Sensitivities and specificities were calculated, and discrimination assessed using the area under the receiver operating characteristic curve (AUC). Forty-nine cases out of 51 nevi and 56/56 melanoma cases had lesional tissue present for p16, while 44/51 nevi and 54/56 melanoma cases had lesional tissue present for PRAME. 43 nodal nevi (88 %) had >50 % nuclear staining for p16, while none had >50 % staining for PRAME. More than half (55 %) of melanoma cases had complete loss of nuclear staining for p16, while majority (94 %) had >50 % nuclear staining for PRAME. Using a cut-off value of 50 %, higher PRAME expression had a sensitivity and specificity of 94 % and 100 %, respectively, while lower p16 expression had a sensitivity and specificity of 66 % and 88 %, respectively, for detecting metastatic melanoma. PRAME showed significantly better discrimination (AUC = 0.97, 95 % CI 0.94–1.00) than p16 (AUC = 0.77, 95 % CI 0.68−0.86) for differentiating nodal nevi from nodal melanoma (P < 0.001). Our findings suggest that PRAME is more accurate than p16 in discriminating between the two entities, with excellent sensitivity and specificity.     

Chromosomal changes in dysplastic nevi.

The dysplastic nevus is considered to be a precursor lesion of melanoma, representing one of the first steps in the progressive transformation from normal melanocyte to melanoma. Various risk degrees of developing cutaneous melanoma in patients with dysplastic nevi have been advanced, based on the presence of dysplastic nevi or melanoma or both in members of the patient's family. We report on the cytogenetic study of three nevi in a young patient with a family history of melanoma. Each nevus showed a simple clonal chromosome change. The t(6;15)(q13;q21) translocation found in one of them seems of particular significance in view of the fact that a similar one, with breakpoint at 6q13 was reported both in an acquired nevus from a patient with a family history of melanoma and in a case of cutaneous metastatic melanoma. These observations seem to support the hypothesis of the existence of a biological continuum between normal melanocyte and melanoma. Furthermore, the finding of chromosome changes similar to those associated with melanoma reinforces the need for a careful follow-up of patients with dysplastic nevi.     

Genetic changes in neoplasms arising in congenital melanocytic nevi: differences between nodular proliferations and melanomas

Large congenital melanocytic nevi (CMN) are at an increased risk of developing melanoma. Several forms of secondary proliferations can arise in congenital nevi on rare occasions. Although some of these closely resemble melanoma both clinically and histologically, metastasis is rare. We used comparative genomic hybridization to analyze chromosomal aberrations in different types of proliferations arising in CMN and compared them to typical congenital nevi, clear-cut melanomas arising in congenital nevi, as well as primary cutaneous melanomas that were not associated with a CMN. Cases of CMN and CMN with secondary proliferations were assigned to six groups according to the predominant histological pattern: group I, bland congenital nevi (n = 6); group II, congenital nevi with foci of increased cellularity (n = 4); group III, CMN with a proliferation simulating superficial spreading melanoma in situ (n = 3); group IV, CMN with a proliferation simulating nodular melanoma (n = 9); group V, proliferating neurocristic hamartoma (n = 1); and group VI, melanoma arising in congenital nevus (n = 6). No aberrations were found in groups I to III, whereas seven of nine cases of group IV, and one of one case of group V, showed aberrations. In group IV six of seven cases with aberrations (86%) showed numerical aberrations of whole chromosomes exclusively. This pattern differed significantly from the findings in melanoma that arose within CMN (n = 6), group VI, or independent of CMN (n = 122) in which only 5% showed numerical changes only. The single case in group V showed aberrations similar to melanoma. The finding of frequent numerical chromosomal aberrations in atypical nodular proliferations arising in CMN identifies these as clonal neoplasms with a genomic instability consistent with a mitotic spindle checkpoint defect. This difference compared to the aberration pattern found in melanoma might explain their more benign clinical behavior and may be of diagnostic value in ambiguous cases.     

Congenital melanocytic nevi of the small and garment type. Clinical, histologic, and ultrastructural studies

The clinical and histologic features of 60 congenital compound and dermalnevi were reviewed and compared to those of 60 acquired compound and dermal nevi. Clinically the two groups could be distinguished by size, most congenital nevi being larger than 1.5 cm. and most acquired nevi smaller than 1.5 cm. in diameter. In addition, congenital nevi commonly are different in coloration and surface topography from acquired nevi. Histologically the congenital nevi had three diagnostic features that separated them from acquired nevi: (1) Nevus cells were present in the lower two thirds of the reticular layer of the dermis in 59 of the 60 cases and in the subcutis as well in 35 cases. (2) Nevus cells were disposed between collagen bundles singly or in Indian files, or both, in all cases. (3) Nevus cells commonly involved appendages, nerves, and vessels in the lower two thirds of the reticular dermis or subcutis and occasionally involved more than one of these structures in the same nevus. Of the 60 compound and dermal nevi present at birth, six were garment (giant hairy) nevi, and their histologic characteristics were similar to those of the other congenital compound and dermal nevi. In light of the increased incidence of malignant melanoma in garment nevi, the distinctive nature of congenital nevi should be borne in mind in order to determine whether other congenital nevi of a smaller size may share in the propensity for malignant degeneration. Although it was not a formal part of the series of cases analyzed in this report, we have observed one case of malignant melanoma that arose in a relatively small congenital nevus.     

Sentinel lymph nodes in cutaneous melanoma: the experience in the Florence area

In the period 1997-2001, 466 sentinel lymph nodes from 342 lymphatic basins in 322 melanoma patients were examined at the Health Unit of Florence. The lymphatic mapping was performed through pre-operative lymphoscintigraphy using technetium-labelled nano-colloid, intradermal injections of vital blue dye and intra-operative gamma-probe. The examined patients were 182 females and 140 males. Sentinel lymph node was one in 65.2% of cases; two sentinel lymph nodes were detected in 27% of cases and more than 2 sentinel nodes were detected in 7.8% of cases. Melanoma metastases in one or more sentinel lymph nodes were found in 61/322 patients (18.9%). Lymphatic basins resulted to be involved by melanoma metastases were 64/342 (18.7%); sentinel lymph nodes containing metastatic melanoma deposits were 73/466 (15.6%). No metastasis was found in patients with melanoma thickness < or = 1 mm. One or more positive sentinel lymph nodes were found in 7.5% of patients with melanoma thickness > 1.00 and < or = 1.50 mm, in 27.7% of patients with melanoma > 1.50 and < or = 3.00 mm, in 38.2% of patients with melanoma > 3.00 and < or = 4.00, and in 60.7% of patients with melanoma > 4.00 mm. Frozen section analysis of sentinel lymph nodes, performed in 59/61 patients with nodal metastases, detected nodal involvement in 21 patients (35.6%). Metastases were identified by routine hematoxylin-eosin staining in 57/64 positive lymphatic basins; in 7 cases (11%) metastases were detected by immunohistochemical stainings (S100 and HMB-45). A nodal nevus was found in 3/466 sentinel lymph nodes (0.6%). Our data are analyzed and compared to previously data of the literature. The value of frozen section analysis and the major problems in the diagnosis of melanoma micrometastases in sentinel lymph nodes are discussed. The importance of the sentinel node biopsy for the detection of occult metastases and for the correct staging of melanoma patients are stressed, according to the new TNM melanoma classification.     

Spitz nevi and atypical Spitz nevi/tumors: a histologic and immunohistochemical analysis.

A subset of Spitz nevi poses substantial diagnostic difficulty, even among experts, due to its resemblance to malignant melanoma. These lesions are termed atypical Spitz nevi/tumors and there is currently a lack of objective criteria for predicting their biologic behavior. We compared the expression of Ki-67, p21, and fatty acid synthase by immunohistochemistry in 10 atypical Spitz nevi, 28 typical Spitz nevi, 19 compound melanocytic nevi and 18 invasive malignant melanomas. There was a progressive increase in fatty acid synthase cytoplasmic expression with statistically significant differences observed between Spitz nevi and atypical Spitz nevi (P=0.003) and between atypical Spitz nevi and malignant melanoma (P<0.050). Ki-67 nuclear staining was lower in both typical and atypical forms of Spitz lesions than in malignant melanoma (P<0.001). The degree of P21 nuclear expression in atypical Spitz nevi was not significantly different than in Spitz nevi, but was significantly greater than expression in conventional nevi and approached significance after multiple comparisons corrections for malignant melanoma. Thus, a high level of P21 expression makes a tumor more likely to be a typical or atypical Spitz nevus than a malignant melanoma, especially when coupled with a low Ki-67 index and weak expression of fatty acid synthase. These immunohistochemical observations support the concept that atypical Spitz nevi are distinct lesions of borderline biologic behavior residing between Spitz nevi and malignant melanoma. The study also compared a large array of histologic features of 16 cases of typical Spitz nevi in children with 12 typical Spitz nevi in adults. The adult lesions were significantly more likely to be intradermal and to display dermal fibroplasia, but were histologically similar to their pediatric counterparts in all other respects.     

Clinical implications of immunohistochemically demonstrated lymph node micrometastasis in resectable pancreatic cancer

The purpose of this study was to determine the clinical significance of nodal micrometastasis detected by immunohistochemistry in patients that had undergone curative surgery for pancreatic cancer. Between 2005 and 2006, a total of 208 lymph nodes from 48 consecutive patients with pancreatic cancer that had undergone curative resection were immunostained with monoclonal antibody against pan-ck and CK-19. Micrometastasis was defined as metastasis missed by a routine H&E examination but detected during an immunohistochemical evaluation. Relations between immunohistochemical results and clinical and pathologic features and patient survival were examined. Nodal micrometastases were detected in 5 (29.4%) patients of 17 pN0 patients. Nodal micrometastasis was found to be related to tumor relapse (P = 0.043). Twelve patients without overt nodal metastasis and micrometastasis had better prognosis than 5 patients with only nodal micrometastasis (median survival; 35.9 vs 8.6 months, P < 0.001). The Cox proportional hazard model identified nodal micrometastasis as significant prognostic factors. Although the number of patients with micrometastasis was so small and further study would be needed, our study suggests that the lymph node micrometastasis could be the predictor of worse survival and might indicate aggressive tumor biology among patients undergoing curative resection for pancreas cancer.     

Angiogenesis and tumor progression of melanoma. Quantification of vascularity in melanocytic nevi and cutaneous malignant melanoma.

BACKGROUND: The capacity of cutaneous malignant melanoma (CMM) to induce angiogenesis is well established. In addition, dysplastic melanocytic nevi (DMN) have been reported to display prominent vascularity relative to common acquired nevi; but this observation has never been verified objectively. EXPERIMENTAL DESIGN: In the following studies, papillary dermal or tumor vascularity was quantified in 10 examples of normal skin, and in a series of 18 melanocytic nevi, 29 DMN, 37 primary CMM and 5 melanoma metastases. Microvessels were identified with the lectin Ulex europaeus agglutinin I. The number of microvessels were counted with an ocular grid (area 7.84 x 10(-2) mm2) at x400 magnification, and the mean vascularity recorded for five fields for each specimen. RESULTS: Mean vascular counts were as follows: normal skin 5.9, common acquired nevus 9.1, nevus with features of DMN 10.3, DMN, slight atypia 11.8; DMN, moderate atypia 12.2; DMN, severe atypia 14.8; primary CMM 25.4; and metastatic melanoma 29.5). Significant differences were recorded for DMN, severe atypia versus melanoma (p less than 0.01), DMN, severe versus common nevi (p less than 0.02) and versus nevi with features of DMN (P less than 0.05). When microvessel counts from CMM in the radial growth phase were compared with those from CMM in the vertical growth phase, or CMM less than 1.0 mm versus those greater than 1.0 mm, no significant differences were found. However, CMM in radial growth did differ from severely atypical DMN (22.4 versus 14.8, p less than 0.05). CONCLUSIONS: These results quantify for the first time a gradual rise in vascularity with tumor progression in the melanocytic system and onset of angiogenesis during the radial growth phase of CMM. Other than severely atypical DMN, DMN did not differ substantially from common nevi with reference to overall vascularity.     

Mutations and copy number increase of HRAS in Spitz nevi with distinctive histopathological features

Spitz nevus is a benign melanocytic neoplasm that can be difficult or impossible to histologically distinguish from melanoma. We have recently described copy number increases of chromosome 11p in a subset of Spitz nevi. To study the molecular and histological features of this group, we studied 102 Spitz nevi for 11p copy number increases using fluorescence in situ hybridization (FISH) on tissue arrays. Copy number increases of at least threefold were found in 12 cases (11.8%) and involved the HRAS gene on chromosome 11p. Sequence analysis of HRAS showed frequent oncogenic mutations in cases with copy number increase (8/12 or 67%), contrasting with rare HRAS mutations in cases with normal HRAS copy numbers (1/21 or 5%, P: < 0.0001). Tumors with 11p copy number increases were larger, predominantly intradermal, had marked desmoplasia, characteristic cytological features, and had an infiltrating growth pattern. Proliferation rates in the majority of these cases were low to absent. HRAS activation by either mutation or copy number increase alone could explain several of the histological features that overlap with those of melanoma. We speculate that HRAS activation in the absence of co-operating additional genetic alterations drives the partially transformed melanocytes of these Spitz nevi into senescence or a stable growth arrest. Although there is no data suggesting that Spitz nevi with HRAS activation are at risk for progression to melanoma, future studies are warranted to assess their biological behavior more accurately.     

Correlation of histologic architectural and cytoplasmic features with nuclear atypia in atypical (dysplastic) nevomelanocytic nevi

The dysplastic nevus in nonfamilial melanoma is a clinicopathologic entity consistently demonstrating an eightfold or greater association with malignant melanoma. The present report quantifies the relationship between nuclear atypia and 16 architectural and cytoplasmic features in 153 pigmented nevi removed from a similar number of patients with newly diagnosed nonfamilial melanoma. All lesions were evaluated by one dermatopathologist, and most lesions were reviewed by a second dermatopathologist. Nuclear atypia of nevomelanocytes was defined as at least three of the following: nuclear enlargement, pleomorphism, hyperchromatism, and prominent nucleoli easily observed throughout each lesion. Seventeen percent of the total nevi had such atypia. On univariate analysis, 11 parameters (lentiginous hyperplasia of the epidermis, basal melanocytic hyperplasia, junctional nest disarray, fusion [bridging] of theques, suprabasal melanocytes, lymphoid response, prominent vascularity, fibroplasia, abundant cytoplasm, "dusty" cytoplasm, and large melanin granules) showed an association with nuclear atypia (P less than .05). However, on multivariate analysis only five parameters continued to be important: basal melanocytic hyperplasia, junctional nest disarray, melanophages (inverse correlation), prominent vascularity, and large melanin granules. These data support the idea that multiple histopathologic characteristics, correlating objectively with nuclear atypia, are important for the diagnosis of dysplastic nevi. In our view, the minimal essential histologic criteria for dysplastic nevi based on these findings include nuclear atypia and abnormal patterns of intraepidermal nevomelanocytic proliferation (ie, basal melanocytic hyperplasia and/or junctional nest disarray).     

Somatic mutations in GNAQ in amelanotic/hypomelanotic blue nevi

A recent study indicates that somatic mutations in codon 209 of GNAQ, a gene encoding the signaling protein G-protein α subunit q, may be present in up to 80% of blue nevi. Given that mutations in GNAQ represent dominant dark skin (Dsk) mutations caused by increased dermal melanin, the primary aim of this study was to ascertain whether amelanotic/hypomelanotic blue nevi exhibited somatic mutations in GNAQ like their melanotic counterpart. Genomic DNA was isolated for genotyping per protocol using techniques including laser capture microdissection to isolate nevus cells from amelanotic/hypomelanotic blue nevi (n = 8). The positive control group comprised regular blue nevi (n = 10, all melanotic) and cellular blue nevi (n = 9, all melanotic), whereas the negative control group comprised other dermal-based nevomelanocytic proliferations such as intradermal melanocytic nevi (n = 9, 7 of which were amelanotic) and metastatic melanoma (n = 9, 5 of which were amelanotic). DNA sequencing analysis was performed on GNAQ spanning codon 209, BRAFV600E, NRAS1, NRAS2, and KRAS genes. Mutations in GNAQ were noted in 12.5% (1/8) of amelanotic/hypomelanotic blue nevi. In the control group 40% (4/10) of blue nevi and 44% (4/9) of cellular blue nevi demonstrated the GNAQ mutation, with no cases of metastatic melanoma or intradermal melanocytic nevi exhibiting the mutation. All GNAQ mutations were A/T point mutations, and statistically significant differences were not noted among the amelanotic/hypomelanotic blue nevi, blue nevi, and cellular blue nevi subgroups. Although additional mutations were not noted in cases of amelanotic/hypomelanotic blue nevi, one blue nevus exhibited a mutation in KRAS alone; one cellular blue nevus, a concurrent NRAS2 mutation; one cellular blue nevus, a concurrent KRAS mutation; and a third cellular blue nevus, a mutation in KRAS alone. The presence of GNAQ mutations in the amelanotic/hypomelanotic blue nevus indicates that mechanisms underlying pigment homeostasis in this variant appear to be similar to those of its melanotic counterparts, although it is not clear why activation of the q class of the G-protein α subunit should cause an abundance of dermal pigment in one variant and not in another. Given that dermal melanocytes are present since birth, one possible explanation is that their melanin-synthesizing pathway is usually in a dormant state. Activation of this pathway is a consequence of multiple triggers-one of which is a mutation in the GNAQ gene, whereas the other is yet to be identified.     

False-positive cells in sentinel lymph nodes

Melanoma sentinel lymph nodes (SLN) are carefully evaluated to maximize sensitivity. Examination includes hematoxylin and eosin (H+E) stained sections at multiple levels through the node, with subsequent immunohistochemical (IHC) stains for melanocytic markers if H+E sections are negative for melanoma. However, not all IHC-positive cells in SLN are metastatic melanoma, as evidenced by the presence of MART-1 positive cells in SLN from breast cancer patients with no history of melanoma (so-called 'false-positive' cells). These 'false-positive cells' could be nodal nevus, non-melanocytic cells with cross-reacting antigenic determinants, phagocytic cells containing melanocyte antigens, or possibly melanocytes or melanocyte stem cells liberated at the time of biopsy of the cutaneous melanoma. Examination of SLN requires careful correlation of H+E and IHC findings.