Quantification of vascularity in nodular melanoma and Spitz's nevus

Fast raster-scan optoacoustic mesoscopy enables assessment of human melanoma microvasculature in vivo

Melanoma is associated with angiogenesis and vascular changes that may extend through the entire skin depth. Three-dimensional imaging of vascular characteristics in skin lesions could therefore allow diagnostic insights not available by conventional visual inspection. Raster-scan optoacoustic mesoscopy (RSOM) images microvasculature through the entire skin depth with resolutions of tens of micrometers; however, current RSOM implementations are too slow to overcome the strong breathing motions on the upper torso where melanoma lesions commonly occur. To enable high-resolution imaging of melanoma vasculature in humans, we accelerate RSOM scanning using an illumination scheme that is coaxial with a high-sensitivity ultrasound detector path, yielding 15 s single-breath-hold scans that minimize motion artifacts. We apply this Fast RSOM to image 10 melanomas and 10 benign nevi in vivo, showing marked differences between malignant and benign lesions, supporting the possibility to use biomarkers extracted from RSOM imaging of vasculature for lesion characterization to improve diagnostics.

Raster-Scanning-Optoacoustic Mesoscopy can be used to image the vasculature in skin cancer lesions but is limited by a long exposure time. Here; the authors increase the speed of the imaging using co-axial illumination and a high-sensitivity ultrasound detector path.

Increased laser Doppler flow in skin tumors corresponds to elevated vessel density and reactive hyperemia

BACKGROUND/PURPOSE

Tumor angiogenesis plays a key role in tumor growth and formation of metastasis. Quantitative analysis of tumor blood flow is a prerequisite for developing novel treatment strategies such as antiangiogenic and antivascular treatment options. Laser Doppler flow in malignant melanomas has been shown to be increased compared with normal skin and melanocytic nevi. This study investigated whether this phenomenon is originated by elevated blood vessel density or by reactive hyperemia.

METHODS

Laser Doppler flow was studied in 35 melanocytic nevi, 22 malignant melanomas and three basal cell carcinomas. After excision digital imaging analysis was performed in microtome sections (factor VIII-associated antigen and CD 31 labelled). The ratio of vessel area in histological sections from tumor tissue and in non-lesional skin was calculated and related to Doppler flow values.

RESULTS

Malignant melanomas demonstrated an enlargement of vessel cross-sectional area by factor 3.7+/-1.9 and of Doppler flow by factor 10.56+/-10.7, and melanocytic nevi accomplished increase of vessel cross-sectional area by factor 1.7+/-0.9 and of Doppler flow by factor 2.7+/-3.5.

CONCLUSION

The laser Doppler flow is influenced by the number and the velocity of erythrocytes in the tissue. The greater increase of laser Doppler flow than of vessel density in histological sections demonstrates that the flow signal in skin tumors is caused by neovascularization as well as by functional hyperemia. Laser Doppler perfusion imaging is a useful method for non-invasive, repeated and quantitative assessment of tumor vascular network and effects of antiangiogenic treatment directed vs. tumor vasculature in vivo, but it cannot distinguish between increased vessel density and reactive hyperemia.

Nodular melanoma: patients' perceptions of presenting features and implications for earlier detection

BACKGROUND

The incidence of thick melanoma and related mortality is largely static despite advances in early detection during the last 20 years. Nodular melanoma (NM) accounts for the majority of thick lesions and is difficult to recognize in the early stages of its evolution.

OBJECTIVE

The purpose of this study was to identify historic or clinical features that may facilitate earlier detection of NM.

METHODS

A questionnaire was administered to 125 patients attending the Victorian Melanoma Service between 1998 and 2000 with superficial spreading melanoma or NM. Parameters were compared by tumor type and thickness.

RESULTS

NMs are more often symmetric, elevated, uniform in color, and nonpigmented. Color change is uncommon.

CONCLUSION

NM often fails to fulfill the ABCD diagnostic criteria. Biopsy after a set period of observation should aid differentiation from inflammatory lesions and enable earlier detection of this subtype.

Tumor vascularization in experimental melanomas: correlation between unenhanced and contrast enhanced power Doppler imaging and histological grading

The purpose of this study was to evaluate the reliability of unenhanced and enhanced power Doppler sonography in visualization of intratumoral angioneogenesis. Thirty-seven malignant melanomas, which had been implanted intra- or subcutaneously in 22 mice, were examined. Various B-mode criteria, power Doppler criteria and spectral Doppler parameters were evaluated before and after IV-application of the d-galactose-based contrast agent Levovist. After sonographic examination, all tumors were analyzed histologically with semiquantitative grading of tumoral vascularization. Unenhanced, in 70% of the tumors, no intratumoral vessels were visible using power Doppler, but only in 11% of the intracutaneous and in 0% of the subcutaneous after injection of the contrast agent. The enhanced mode was definitely superior to unenhanced Doppler in showing the intratumoral vascularity. The intratumoral vascular structure could be sufficiently analyzed in 30% of all tumors by unenhanced Doppler, but in 92% enhanced. The mean percentage vessel area increased about 433% after application of Levovist (intracutaneous: 485%, subcutaneous: 280%). Despite the missing direct correlation between the sonographically and histologically determined grade of tumor vascularization (Pearson's correlation unenhanced 0,356, p <.05/enhanced 0.395, p <.05), the correlation between the percentage vessel area and the histologic grade of vascularization was improved after application of the contrast agent (Pearson's correlation unenhanced 0.347, p <.05/enhanced 0.686, p <.01). We did not find a significant direct correlation between histologically and sonographically determined degree of vascularization. However, the correlation was improved using a d-galactose-based signal-enhancing agent in power Doppler sonography.

Vasculogenic mimicry and tumor angiogenesis

Tumors require a blood supply for growth and hematogenous dissemination. Much attention has been focused on the role of angiogenesis-the recruitment of new vessels into a tumor from pre-existing vessels. However, angiogenesis may not be the only mechanism by which tumors acquire a microcirculation. Highly aggressive and metastatic melanoma cells are capable of forming highly patterned vascular channels in vitro that are composed of a basement membrane that stains positive with the periodic acid-Schiff (PAS) reagent in the absence of endothelial cells and fibroblasts. These channels formed in vitro are identical morphologically to PAS-positive channels in histological preparations from highly aggressive primary uveal melanomas, in the vertical growth phase of cutaneous melanomas, and in metastatic uveal and cutaneous melanoma. The generation of microvascular channels by genetically deregulated, aggressive tumor cells was termed "vasculogenic mimicry" to emphasize their de novo generation without participation by endothelial cells and independent of angiogenesis. Techniques designed to identify the tumor microcirculation by the staining of endothelial cells may not be applicable to tumors that express vasculogenic mimicry. Although it is not known if therapeutic strategies targeting endothelial cells will be effective in tumors whose blood supply is formed by tumor cells in the absence of angiogenesis, the biomechanical and molecular events that regulate vasculogenic mimicry provide opportunities for the development of novel forms of tumor-targeted treatments. The unique patterning characteristic of vasculogenic mimicry provides an opportunity to design noninvasive imaging techniques to detect highly aggressive neoplasms and their metastases.

Polypoid Spitz naevus: the benign counterpart of polypoid malignant melanoma

Polypoid malignant melanoma is a peculiar morphological variant of melanoma with a distinct exophytic pattern of growth. This form of melanoma is usually very thick and the prognosis is accordingly poor. We present here a previously undescribed form of Spitz naevus which had a similar polypoid exophytic silhouette and marked cytological atypia. Despite these close morphological similarities, polypoid Spitz naevus evolves in a completely benign manner. Morphologically, polypoid Spitz naevus can be distinguished from polypoid melanoma by the absence of mitoses and by the prominent stromal reaction throughout the lesion.

The melanocyte differentiation pathway in spitz nevi

The nature of Spitz nevi is poorly understood, and their distinction from malignant melanoma can be difficult. Although there is general agreement on the diagnostic criteria, experts continue to have some differences, and controversial cases are not rare. A major obstacle to progress in this area is the lack of basic knowledge about melanocyte differentiation in Spitz nevi, as compared with ordinary nevi and malignant melanomas. Based on the hypothesis that normal melanocytes may have a differentiation pathway with discrete stages, it is suggested that the features of Spitz nevi may reflect homeostatic mechanisms governing maturation in the melanocyte differentiation pathway, whereas those of malignant melanomas may reflect carcinogen-induced aberrations. This perspective may be helpful in the continuing effort to develop optimal criteria for the differential diagnosis of Spitz nevi from malignant melanomas.