Survival differences between patients with scalp or neck melanoma and those with melanoma of other sites in the Surveillance, Epidemiology, and End Results (SEER) program

OBJECTIVE

To compare the prognosis of patients with scalp or neck (scalp/neck) melanomas with that of patients with melanomas at other sites in a large, population-based national data set controlling for known prognostic factors.

DESIGN

Retrospective cohort study using US cancer registries that constitute the Surveillance, Epidemiology, and End Results 13 Registries (SEER-13) database.

PATIENTS

A total of 51 704 non-Hispanic white adults in the United States with a first invasive cutaneous melanoma reported during the period 1992 to 2003.

MAIN OUTCOME MEASURES

Kaplan-Meier survival estimates were used to compare melanoma-specific survival by anatomic site at 5 and 10 years. Multivariate Cox models were used to examine the hazard ratio (HR) of melanoma-specific death associated with scalp/neck melanoma compared with melanoma of the extremities after controlling for other variables.

RESULTS

The 5- and 10-year Kaplan-Meier survival probabilities for scalp/neck melanoma were 83.1% and 76.2%, respectively, compared with 92.1% and 88.7%, respectively, for melanoma of the other sites, including extremities, trunk, face, and ears (log-rank test; P < .001). In a multivariate Cox model, the patients with melanoma of the scalp/neck died of melanoma at 1.84 times (HR, 1.84; 95% confidence interval, 1.62-2.10) the rate of those with melanoma on the extremities, controlling for age, Breslow thickness, sex, and ulceration. Neither excluding cases of lentigo maligna and nodular melanoma nor controlling for lymph node involvement materially changed the HR for scalp/neck melanoma.

CONCLUSIONS

A notable survival difference remained between scalp/neck melanoma and melanoma of other sites even after adjustment for important prognostic factors. This finding has implications for screening and public health recommendations, and we urge physicians, physician assistants, nurses, and nurse practitioners to examine the scalp/neck carefully during routine skin examinations. Further studies are needed to understand the biological or environmental factors leading to survival differences by anatomic site.

CD200 is induced by ERK and is a potential therapeutic target in melanoma

Immune-mediated antitumor responses occur in patients with metastatic melanoma (MM), and therapies designed to augment such responses are clinically beneficial. Despite the immunogenicity of melanoma, immunomodulatory therapies fail in the majority of patients with MM. An inability of DCs to sufficiently activate effector cells may, in part, underlie this failure of the antitumor response seen in most patients. In this work, we show that mutation of N-RAS or B-RAF, signature genetic lesions present in most MMs, potently induced the expression of cell-surface CD200, a repressor of DC function. Employing 2 independent, genome-wide microarray analyses, we identified CD200 as a highly dynamic, downstream target of RAS/RAF/MEK/ERK activation in melanoma. CD200 protein was similarly overexpressed in human melanoma cell lines and primary tumors. CD200 mRNA expression correlated with progression and was higher in melanoma than in other solid tumors or acute leukemia. Melanoma cell lines expressing endogenous CD200 repressed primary T cell activation by DCs, while knockdown of CD200 by shRNA abrogated this immunosuppressive effect. These data indicate that in addition to its effects on growth, survival, and motility, ERK activation in MM attenuates a host antitumor immune response, implicating CD200 and its interaction with the CD200 receptor as a potential therapeutic target for MM.

Context-dependent roles of mutant B-Raf signaling in melanoma and colorectal carcinoma cell growth

Mutational activation of Ras and a key downstream effector of Ras, the B-Raf serine/threonine kinase, has been observed in melanomas and colorectal carcinomas. These observations suggest that inhibition of B-Raf activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase (MEK) and the extracellular signal-regulated kinase MAPK cascade may be an effective approach for the treatment of RAS and B-RAF mutation-positive melanomas and colon carcinomas. Although recent studies with interfering RNA (RNAi) and pharmacologic inhibitors support a critical role for B-Raf signaling in melanoma growth, whether mutant B-Raf has an equivalent role in promoting colorectal carcinoma growth has not been determined. In the present study, we used both RNAi and pharmacologic approaches to further assess the role of B-Raf activation in the growth of human melanomas and additionally determined if a similar role for mutant B-Raf is seen for colorectal carcinoma cell lines. We observed that RNAi suppression of mutant B-Raf(V600E) expression strongly suppressed the anchorage-dependent growth of B-RAF mutation-positive melanoma, but not colorectal carcinoma, cells. However, the anchorage-independent and tumorigenic growth of B-RAF mutation-positive colorectal carcinomas was dependent on mutant B-Raf function. Finally, pharmacologic inhibition of MEK and Raf was highly effective at inhibiting the growth of B-RAF mutation-positive melanomas and colorectal carcinoma cells, whereas inhibitors of other protein kinases activated by Ras (AKT, c-Jun NH(2)-terminal kinase, and p38 MAPK) were less effective. Our observations suggest that Raf and MEK inhibitors may be effective for the treatment of B-RAF mutation-positive colorectal carcinomas as well as melanomas.

Distance to diagnosing provider as a measure of access for patients with melanoma

OBJECTIVE

To examine the effect of travel distance and other sociodemographic factors on access to a diagnosing provider for patients with melanoma.

DESIGN

Analysis was performed of all incident cases of melanoma in 2000 from 42 North Carolina counties.

SETTING

Academic research.

PARTICIPANTS

Patients and providers from 42 North Carolina counties were geocoded to street address.

MAIN OUTCOME MEASURES

Associations between Breslow thickness and clinical and sociodemographic factors (age, sex, poverty rate, rurality, provider supply, and distance to diagnosing provider) were examined.

RESULTS

Of 643 eligible cases, 4.4% were excluded because of missing data. The median Breslow thickness was 0.6 mm (range, 0.1-20.0 mm). The median distance to diagnosing provider was 8 miles (range, 0-386 miles). For each 1-mile increase in distance, Breslow thickness increased by 0.6% (P =.003). For each 1% increase in poverty rate, Breslow thickness increased by 1% (P =.04). Breslow thickness was 19% greater for patients aged 51 to 80 years than for those aged 0 to 50 years (P =.02) and was 109% greater for patients older than 80 years than for those aged 0 to 50 years (P < .001). Sex, rurality, and supply of dermatologists were not associated with Breslow thickness.

CONCLUSIONS

For patients with melanoma, distance to the diagnosing provider is a meaningful measure of access that captures different information than community-level measures of rurality, provider supply, and socioeconomic status. Future work should be targeted at identifying factors that may affect distance to diagnosing provider and serve as barriers to melanoma care.

Defective cell cycle checkpoint functions in melanoma are associated with altered patterns of gene expression

Defects in DNA damage responses may underlie genetic instability and malignant progression in melanoma. Cultures of normal human melanocytes (NHMs) and melanoma lines were analyzed to determine whether global patterns of gene expression could predict the efficacy of DNA damage cell cycle checkpoints that arrest growth and suppress genetic instability. NHMs displayed effective G1 and G2 checkpoint responses to ionizing radiation-induced DNA damage. A majority of melanoma cell lines (11/16) displayed significant quantitative defects in one or both checkpoints. Melanomas with B-RAF mutations as a class displayed a significant defect in DNA damage G2 checkpoint function. In contrast the epithelial-like subtype of melanomas with wild-type N-RAS and B-RAF alleles displayed an effective G2 checkpoint but a significant defect in G1 checkpoint function. RNA expression profiling revealed that melanoma lines with defects in the DNA damage G1 checkpoint displayed reduced expression of p53 transcriptional targets, such as CDKN1A and DDB2, and enhanced expression of proliferation-associated genes, such as CDC7 and GEMININ. A Bayesian analysis tool was more accurate than significance analysis of microarrays for predicting checkpoint function using a leave-one-out method. The results suggest that defects in DNA damage checkpoints may be recognized in melanomas through analysis of gene expression.

Number of Nevi and Early-Life Ambient UV Exposure Are Associated with BRAF-Mutant Melanoma

Malignant melanomas often contain BRAF or NRAS mutations, but the relationship of these mutations to ambient UV exposure in combination with phenotypic characteristics is unknown. In a population-based case series from North Carolina, 214 first primary invasive melanoma patients in the year 2000 were interviewed regarding their risk factors. Ambient solar UV exposures were estimated using residential histories and a satellite-based model. Cases were grouped on the basis of BRAF and NRAS somatic mutations, determined using single-strand conformation polymorphism analysis and radiolabeled DNA sequencing, and the risk profiles of these groups were compared. Mutually exclusive BRAF-mutant and NRAS-mutant cases occurred at frequencies of 43.0% and 13.6% with mean ages at diagnosis of 47.3 and 62.1 years, respectively. Tumors from patients with >14 back nevi were more likely to harbor either a BRAF mutation [age-adjusted odds ratio (OR), 3.2; 95% confidence interval (95% CI), 1.4-7.0] or an NRAS mutation (age-adjusted OR, 1.7; 95% CI, 0.6-4.8) compared with patients with 0 to 4 back nevi. However, BRAF-mutant and NRAS-mutant tumors were distinctive in that BRAF-mutant tumors were characteristic of patients with high early-life ambient UV exposure (adjusted OR, 2.6; 95% CI, 1.2-5.3). When ambient UV irradiance was analyzed by decadal age, high exposure at ages 0 to 20 years was associated with BRAF-mutant cases, whereas high exposure at ages 50 and 60 years was characteristic of NRAS-mutant cases. Our results suggest that although nevus propensity is important for the occurrence of both BRAF and NRAS-mutant melanomas, ambient UV irradiance influences risk differently based on the age of exposure. The association of BRAF mutations with early-life UV exposure provides evidence in support of childhood sun protection for melanoma prevention.

RNA expression analysis of formalin-fixed paraffin-embedded tumors

RNA expression analysis is an important tool in cancer research, but a limitation has been the requirement for high-quality RNA, generally derived from frozen samples. Such tumor sets are often small and lack clinical annotation, whereas formalin-fixed paraffin-embedded (FFPE) materials are abundant. Although RT-PCR-based methods from FFPE samples are finding clinical application, genome-wide microarray analysis has proven difficult. Here, we report expression profiling on RNA from 157 FFPE tumors. RNA was extracted from 2- to 8-year-old FFPE or frozen tumors of known and unknown histologies. Total RNA was analyzed, reverse-transcribed and used for the synthesis of labeled aRNA after two rounds of amplification. Labeled aRNA was hybridized to a 3'-based 22K spot oligonucleotide arrays, and compared to a labeled reference by two-color microarray analysis. After normalization, gene expression profiles were compared by unsupervised hierarchical clustering. Using this approach, at least 24% of unselected FFPE samples produced RNA of sufficient quality for microarray analysis. From our initial studies, we determined criteria based on spectrophotometric analyses and a novel TaqMan-based assay to predict which samples were of sufficient quality for microarray analysis before hybridization. These criteria were validated on an independent set of tumors with a 100% success rate (20 of 20). Unsupervised analysis of informative gene expression profiles distinguished tumor type and subtype, and identified tumor tissue of origin in three unclassified carcinomas. Although only a minority of FFPE blocks could be analyzed, we show that informative RNA expression analysis can be derived from selected FFPE samples.

Eruptive post-chemotherapy in situ melanomas and dysplastic nevi

A 22-year-old white man without a personal or family history of atypical nevi had received chemotherapy for pre-B-cell acute lymphocytic leukemia at age 17 that included L-asparaginase, prednisone, methotrexate, mercaptopurine, daunorubicin, and cytoxan. Two to three months after completing maintenance chemotherapy, the patient reports he developed many moles, which remained stable for approximately 2 years. Upon examination, two dark, atypical appearing plaques with irregular borders and numerous pink papules of varying shapes and sizes were noted on his chest, back, and abdomen. Histology of specimens of both types of lesions revealed three moderately atypical compound dysplastic melanocytic nevi and three in situ melanomas. The lesions with only features of dysplastic nevi exhibited dermal fibrosis, cytologic atypia, junctional shoulders, lentiginous spread, and focal pigmentation. The lesions with in situ melanomas in addition demonstrated pagetoid spread, extension down adnexal structures, and more severe cytologic atypia. Malignant melanoma has been associated with chronic immunosuppression, and benign nevi have been reported to erupt after chemotherapy. We report an occurrence of multiple eruptive dysplastic nevi and in situ melanomas appearing shortly after completion of chemotherapy.

Lack of Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase Signaling Shows a New Type of Melanoma

The majority of human melanomas harbor activating mutations of either N-RAS or its downstream effector B-RAF, which cause activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase and the ERK MAPK cascade. The melanoma-relevant effectors of ERK activation, however, are largely unknown. In this work, we show that increased ERK activation correlates strongly with mutational status of N-RAS or B-RAF in 21 melanoma cell lines. Melanoma lines that were wild-type for RAS/RAF showed low levels of ERK activation comparable with primary human melanocytes. Through supervised analysis of RNA expression profiles, we identified 82 genes, including TWIST1, HIF1alpha, and IL-8, which correlated with ERK activation across the panel of cell lines and which decreased with pharmacologic inhibition of ERK activity, suggesting that they are ERK transcriptional targets in melanoma. Additionally, lines lacking mutations of N-RAS and B-RAF were molecularly distinct and characterized by p53 inactivation, reduced ERK activity, and increased expression of epithelial markers. Analysis of primary human melanomas by tissue microarray confirmed a high correlation among expression of these epithelial markers in a heterogeneous sample of 570 primary human tumors, suggesting that a significant frequency of primary melanomas is of this "epithelial-like" subtype. These results show a molecularly distinct melanoma subtype that does not require ERK activation or epithelial-mesenchymal transformation for progression.

Influence of provider and practice characteristics on melanoma care

BACKGROUND

Melanoma care is becoming increasingly multidisciplinary, requiring coordination of many types of providers. The purpose of this study is to describe the structure of melanoma care in North Carolina by examining services provided by different providers and the overall coordination of care.

METHODS

Self-administered surveys were developed to collect demographic and practice information, assess patient volume and services provided, and explore referral patterns. Surveys were administered to all dermatologists and a subset of surgeons practicing in North Carolina.

RESULTS

The response rate was 60% (263/438). Melanoma patient volume, referral patterns, use of nodal staging, and access to clinical trials were each related to provider characteristics, specialty, affiliations with cancer care organizations, and practice setting.

CONCLUSIONS

Many types of providers contribute significantly to the care of melanoma patients. Coordination between providers is variable. This study provides indirect evidence that multidisciplinary melanoma programs increase patient access to comprehensive melanoma care.

Muir-Torre syndrome

In this case report of Muir-Torre syndrome (MTS), we describe a 47-year-old man with a personal and family history of colon cancer and a personal history of keratoacanthoma who presented with a sebaceous carcinoma and, subsequently, had a cystic sebaceous tumor. Immunohistochemical examination of the patient's colonic tumor, located proximal to the splenic flexure, revealed absence of MutL homolog (MLH)-1 protein. MTS is a rare genodermatosis defined clinically by the occurrence of a sebaceous neoplasm and an internal malignancy in the absence of other predisposing factors. Most patients present with sebaceous adenomas, but cystic sebaceous neoplasms have been reported as specific markers of MTS. Gastrointestinal and genitourinary cancers are the most common internal malignancies, with colorectal cancers often occurring at or proximal to the splenic flexure, contrary to most sporadic colorectal cancers. MTS is most frequently found as a variant of the autosomal dominant disorder hereditary non-polyposis colorectal cancer (HNPCC), with tumors demonstrating microsatellite instability and germline mutations in the DNA mismatch repair genes MutS homolog (MSH)-2 and MLH1. However, the distribution of gene mutations of patients with MTS is slightly different from that seen in all HNPCC families, and some cases of MTS arise spontaneously. Physicians should consider MTS in patients presenting with a sebaceous neoplasm, and immunohistochemical examination of tumors for MSH2 and MLH1 protein can be used as a screening test to identify patients with MTS. While the sebaceous and internal neoplasms of MTS are thought to follow a more indolent course than sporadic malignancies, patients with this disorder should be treated with standard therapies and carefully followed. Evidence indicates that for individuals with or at risk of MTS or HNPCC, colonoscopy every 1-2 years beginning at age 20-25 or 10 years younger than the youngest age at diagnosis in the family can be strongly recommended. Additionally, most experts believe that an annual history and physical examination, including a complete skin examination and urinalysis, as well as periodic endometrial sampling and/or transvaginal ultrasound for women, are worthwhile screening tests for these high-risk patients.

Treatment of gefitinib-associated folliculitis

Gefitinib (Iressa), an epidermal growth factor inhibitor approved for treatment of advanced nonsmall cell lung carcinoma, is associated with an acneiform distributed folliculitis. Treatment attempts for this folliculitis have been noted in the literature, but photodocumentation of results has not been reported. We report 3 consecutive cases of gefitinib-associated folliculitis with photodocumentation of their treatment responses to combination therapy with topical metronidazole and oral tetracyclines.

BRAF and NRAS mutations in melanoma and melanocytic nevi

In this report, we investigated BRAF/NRAS mutations in samples from a case-control study of melanoma and a series of benign melanocytic nevi. We evaluated potential associations between BRAF mutations and histopathologic and pigmentary characteristics of melanoma. Mutations in BRAF and NRAS were detected by sequencing microdissected/laser-captured DNA from 18 in-situ melanomas, 64 primary melanomas, and 51 nevi. Nevi showed the highest frequency of BRAF mutations (82%). BRAF mutations were identified in 29% of invasive melanomas and in only 5.6% of in-situ melanomas. Mutations in NRAS were found in 5.2% of primary melanomas, 5.9% of nevi and no NRAS mutations were seen in in-situ melanomas. A majority of the BRAF mutations observed in primary invasive melanoma were seen in superficial spreading melanoma (15/17), and melanomas with BRAF mutations were also more likely to be found on a body site that was likely to be exposed to intermittent sun exposure compared with chronic or no sun exposure (P=0.02). Tumors with BRAF mutations were also significantly more likely to occur in association with a contiguous nevus (odds ratio 3.49, 95% confidence interval 1.06-11.46), although a contiguous nevus was not found in all melanomas with a BRAF mutation. Our data support the evidence that the mitogen-activated protein kinase pathway is upregulated in a large percentage of melanocytic lesions, but these mutations are not sufficient for malignant transformation. We suggest that BRAF mutations contribute to benign melanocytic hyperplasia, but are likely to contribute to invasive melanoma only in conjunction with other mutations.

Could BRAF Mutations in Melanocytic Lesions Arise from DNA Damage Induced by Ultraviolet Radiation?

Although BRAF V600 mutations in melanocytic tumors are not UV-signature mutations, it is plausible that they could still arise from error-prone replication of UV-damaged DNA. We propose a mechanism for their origin, taking into consideration melanocytic-specific BRAF tandem mutations, nearby potential pyrimidine dimer sites, the properties of specialized DNA polymerases, and biological selection.

BRAF somatic mutations in malignant melanoma and melanocytic naevi

BRAF somatic mutations are frequently found in primary and metastatic melanomas and melanocytic naevi. Commonly found BRAF mutants stimulate constitutive RAF/MEK (mitogen-activated ERK-activating kinase)/ERK (extracellular signal-regulated kinase) pathway activation and act as transforming oncogenes in NIH-3T3 cells and immortalized murine melanocytes. The most common BRAF mutation is the V600E alteration, but over 30 distinct BRAF mutations, varying in biological activity, have been found and may be predictive of clinically relevant tumour differences. The origin of these acquired mutations remains unknown, but melanomas have a different BRAF mutational spectrum from other tumours, possibly resulting from unique environmental exposures. In melanoma cases, BRAF mutations are frequently found in superficial spreading or nodular histological subtypes, in tumours on intermittently sun-exposed sites and in younger patients. Although evidence indicates that the activation of the RAF/MEK/ERK pathway influences the proliferation, invasion and survival of melanoma cells in vitro, the exact role of BRAF mutation in melanoma tumour progression, maintenance and outcome remains controversial. In addition, although BRAF and NRAS mutations are mutually exclusive in melanomas, other genetic events may complement BRAF mutation to produce biological activity similar to NRAS mutation. Nonetheless, preclinical and early clinical studies predict that RAF/MEK/ERK pathway inhibitors will have therapeutic activity towards melanoma, but that tumour subclassification by BRAF/NRAS mutational status may be necessary to evaluate their efficacy.

Population-based analysis of lymphatic mapping and sentinel lymphadenectomy utilization for intermediate thickness melanoma

BACKGROUND AND OBJECTIVES

Lymphatic mapping and sentinel lymphadenectomy (LM/SL) is the nodal staging procedure of choice for patients with intermediate thickness melanoma. We hypothesize that a significant portion of these patients are not undergoing LM/SL. We explore factors that influence use of LM/SL.

METHODS

Analysis was performed of all incident cases of invasive cutaneous melanoma in North Carolina between January 1, 1999 and December 31, 2001.

RESULTS

Three thousand four hundred and thirty-six cases of melanoma were reported for 1999-2001. Two hundred and seventy-three cases (8%) were excluded due to metastases. Nine hundred and sixteen cases (29%) were excluded because the T classification was not reported. Of the remaining cases, 1,242 (55%) were intermediate thickness (T2-3); 48% (596/1,242) underwent LM/SL. Subjects >or=60 years old were less likely to receive LM/SL than subjects <60 years (39% vs. 55.4%, P < 0.001). Subjects with head/neck primary tumors were less likely to receive LM/SL than other subjects (33% vs. 51%, P < 0.001). Subjects with T3 tumors were more likely to receive LM/SL than those with T2 tumors (54% vs. 42%, P < 0.001).

CONCLUSIONS

Half of all patients with intermediate thickness melanoma in North Carolina do not receive LM/SL. Use of LM/SL varies by patient age and primary tumor site. Further investigation is warranted to explore these differences.

Invasive superficial spreading melanomas arising from clinically normal skin

We provide documentation of the onset of 3 invasive superficial spreading melanomas arising from clinically normal skin and correlation with histologic lack of nevus association. Clinical, dermoscopic, and pathologic features of these "de novo" melanomas, which became invasive while small in diameter and had few clinical criteria for diagnosis, are reported.

Indications for lymphatic mapping and sentinel lymphadenectomy in patients with thin melanoma (Breslow thickness < or =1.0 mm)

BACKGROUND

Patients with thin (Breslow thickness < or =1.0 mm) melanoma have a good prognosis (5-year survival >90%). Consequently, the added benefit of lymphatic mapping and sentinel lymphadenectomy (LM/SL) in these patients is controversial. We hypothesize that LM/SL with a focused examination of the sentinel node (SN) will detect a significant number of SN metastases in patients with thin melanoma and that certain clinical or histopathologic factors may serve as predictors of SN tumor involvement.

METHODS

Over 6 years, 349 patients with melanoma underwent LM/SL and were prospectively entered into an institutional review board (IRB)-approved database. LM/SL was performed with a combined radiotracer and blue dye technique. SNs were serially sectioned, and each section was examined by a dermatopathologist at multiple levels with hematoxylin and eosin as well as immunohistochemical stains.

RESULTS

One hundred forty-six patients (42%) had a melanoma with Breslow thickness < or =1.0 mm; six (4%) of these 146 patients had a tumor-involved SN. On multivariate analysis, none of the clinical or histopathologic factors examined were significantly associated with SN tumor involvement in patients with thin melanoma. Completion lymphadenectomy was performed on all patients with a tumor-involved SN. None of the patients had non-SN tumor involvement.

CONCLUSIONS

The incidence of SN tumor involvement in patients with thin melanoma is considerable. Although we were unable to identify predictors of SN tumor involvement in patients with thin melanoma, efforts to identify predictors of SN tumor involvement should continue. Until better predictors are identified, we continue to advocate offering LM/SL to patients with thin melanomas who demonstrate clinical or histopathologic characteristics that have historically been associated with an increased risk of recurrence and mortality.

Tandem BRAF Mutations in Primary Invasive Melanomas

The RAS/RAF/MAPK pathway likely mediates critical cell proliferation and survival signals in melanoma. BRAF mutations have been found in a high percentage of melanoma cell lines and metastases; however, only a few studies with a limited number of specimens have focused on primary melanomas. We examined BRAF exon 15 mutational status in 37 primary invasive melanomas of varying thicknesses, which had undergone a standardized pathology review. BRAF mutational status was determined using direct manual sequencing of PCR products, followed by resequencing separately amplified DNA aliquots to confirm each mutation. BRAF exon 15 mutations were found in 17 of 37 (46%) primary melanomas. Tumor-specific tandem mutations, encoding either V599K, V599R, or V599E, were found in 5 of 17 (29%) melanomas with BRAF exon 15 mutations. Cloning of BRAF double base-pair substitutions confirmed that both base changes were on the same allele and can result in a positive charge at codon 599. BRAF mutations, including tandem mutations, were frequently found in both thin and thick primary melanomas, implying that these mutations can occur early in the progression of melanoma. The finding of tandem mutations in thin melanomas makes it more likely that they arise as a simultaneous rather than sequential event.

Sub-micron particle manipulation in an ultrasonic standing wave: applications in detection of clinically important biomolecules

Separation of particles from the suspending phase is of interest, among others, to clinical analysts. A system that enables manipulation of sub-micron sized particles in suspensions of analytical scale volume (10-50 microl) using a non-cavitating ultrasonic standing wave is described. Particle suspensions, contained in glass capillary tubes of 1-2 mm internal dimension, are treated on the axis of a tubular transducer generating a radial standing wave field at 4.5 MHz. Microparticles (of average diameter range 0.3-10 microm) suspended in buffer are concentrated within seconds at preferred regions separated by submillimetre distances. Concentration of suspended latex particles was inhibited in solutions containing protein at levels similar to those occurring in clinical specimens when the suspensions were sonicated in capillaries of circular cross-section. This effect was associated with acoustic streaming of the suspending fluid. Silica microparticles (more dense and less compressible than latex) could be concentrated in the presence of streaming. Latex particles concentrated readily in square cross-section capillaries where no streaming was observed. With sub-micron particles, the geometry of the sample chamber, the suspending phase composition and the size, density and compressibility of the microparticles all influence particle manipulation. The radial standing wave system has been used to enhance agglutination of antibody-coated latex microparticles in the presence of antigen allowing rapid and highly sensitive detection of clinically important biomolecules. The sensitivity of conventional diagnostic tests for microbial antigen has been improved by application of ultrasound and clinical utility has been demonstrated, in particular, for detection of meningitis-causing bacteria.

Rhodnius prolixus infected with Trypanosoma rangeli: In vivo and in vitro experiments

Studies were carried out on the activation of the prophenoloxidase (proPO) in adults of Rhodnius prolixus infected by short and long epimastigote forms of Trypanosoma rangeli. The in vitro activation of the proPO cascade using l-DOPA as substrate was very low in the absence of fat body extract, hemolymph, and parasites. On the other hand, a higher PO activity was observed when short, but not long, epimastigotes of T. rangeli were incubated with fresh hemolymph, fat body extract, and l-DOPA. Supernatant from lysed long epimastigotes increased the PO activity at levels identical to those observed with supernatants from lysed short epimastigotes. Similarly, the PO activity of hemolymph obtained from inoculated insects with long epimastigotes of T. rangeli showed a very low activity when incubated with l-DOPA compared to the PO activity of hemolymph taken from insects inoculated with short epimastigotes of T. rangeli. Control insects inoculated with sterile PBS showed no PO activity. These data indicate the presence of (a) factor(s) in the hemolymph as well as in the fat body extract that may be released (or induced) by the presence of short epimastigotes of T. rangeli and which results in the activation of the R. prolixus proPO system. The implications of these findings are discussed in relation to the development of T. rangeli and its ability to overcome the proPO system, survive, and successfully colonize the hemolymph of R. prolixus.

Ultrasonic enhancement of coated particle agglutination immunoassays: influence of particle density and compressibility

The detection rate and sensitivity (analyte concentration limit) of coated particle agglutination immunoassays are increased in ultrasonic standing waves. The influence of particle volume, density and compressibility, properties that modify the ultrasonic radiation, and interaction forces the particles experience, on assay sensitivity with latex and silica particles in the range 0.25-1.0 microm is examined here. Streptavidin-coated 0.3-microm silica particles and 0.25-microm and 1.0-microm latex particles were examined for agglutination with biotinylated bovine serum albumin (bBSA) following exposure on axis in a 4.6-MHz radial standing wave. The lowest detection limit, 2 ng/mL bBSA, was achieved with the 0.3-microm silica. The detection limit decreased with increasing latex particle size. The limit of an ultrasound-enhanced agglutination immunoassay of rabbit antimouse immunoglobulin was 6-fold better with 1.0-microm coated silica than with equal-sized latex particles. Calculations show that the particle density-dependent ultrasonic interaction force dominates the particle compressibility force for the present case. The density-dependent force on silica, but not on latex particles, is shown to be comparable in magnitude to both the long-range van der Waal's attractive force and the electrostatic repulsion between the particles. This density-dependent force may explain the improved enhancement of analyte detection by coated silica compared with latex particles.

Measurement of antigen concentration by an ultrasound-enhanced latex immunoagglutination assay

A novel ultrasonic technique that increases the rate and sensitivity of latex agglutination tests (LATs) has recently been described. The technique is based on the fact that suspended latex particles become concentrated in an ultrasonic standing wavefield, thereby increasing the rate of particle-particle collisions compared to the standard LAT procedure. The present work extends earlier qualitative assessments of agglutination and seeks to establish whether quantitative measurement of agglutinate size may be used as an indicator of antigen concentration. The agglutination of latex microparticles coated with antibody to C-reactive protein (CRP) is studied here as a model system to determine the dependence of agglutinate size on analyte (CRP) concentration. Agglutinate size is characterised by image analysis techniques. The results show that agglutinate size decreases with decreasing CRP concentration. A near linear relationship is shown between analyte concentration and the size of agglutinate formed over a 100-fold dilution range. The threshold concentration of 230 pg/mL for detection of CRP in the ultrasonic test is 2560 times lower than that required for a conventional test-card CRP latex agglutination assay.