Apparent absence of a benign precursor lesion: implications for the pathogenesis of malignant melanoma

Clinical presentations of cutaneous melanoma

Cutaneous melanoma is responsible for the majority of skin cancer deaths. Early and accurate detection are the most important means to improve patient survival. This article reviews the common clinical presentations of head and neck cutaneous melanoma, and discusses lesions that might be clinically mistaken for melanoma.

Melanomas in renal transplant recipients

BACKGROUND

It is well documented that renal transplant recipients are at increased risk of developing skin cancers, in particular squamous cell carcinomas. Less extensively reviewed in the literature is the increased incidence of malignant melanoma. We have reviewed 10 patients in the Oxford renal transplant population who developed 12 melanomas following transplantation.

OBJECTIVES

To determine the incidence and characteristics of melanoma in renal transplant recipients.

METHODS

We reviewed the case notes and pathology of all patients who developed melanoma within the Oxford Renal Transplant Unit. The clinical details were recorded including date of transplant, immunosuppressive therapy, interval between transplant and melanoma, site of occurrence, history of sun exposure, type of clinician diagnosing the melanoma, history of other skin malignancies and outcome. From the histopathology we documented various prognostic factors.

RESULTS

Ten patients developed 12 melanomas (one patient had three melanomas) from a population of 1874 transplanted patients. The total number of transplant years was 11 942.2. The incidence of melanoma in our population was 12 per 11 942.2 transplant years, which is approximately 8 times greater than the standardized rate for this region. We found that the mean interval between transplant and melanoma was approximately 11 years (median 8.5). A dermatologist was the diagnosing clinician in at least 67% of cases. Melanomas occurred on the trunk in the majority of cases (58%), followed by the upper limb (25%). All patients apart from one are alive with no recurrence of their melanoma. One patient died as a result of metastatic melanoma. The mean follow-up period following melanoma was 3.7 years. In all patients apart from the patient who died, the melanomas were < 1 mm Breslow thickness. That patient's melanoma was 4.5 mm thick. There was no precursor naevus in eight of the 12 melanomas. In two there was a precursor dysplastic naevus. In the cases in vertical growth phase the tumour-infiltrating lymphocyte response was absent in four cases and nonbrisk in one patient.

CONCLUSIONS

In the Oxford transplant population studied melanomas occurred at approximately 8 times the rate in the general population. This is the highest rate reported in the literature. The patients had a better outcome than reported previously. This may be due to detection at a relatively early stage. Renal transplant recipients attend dedicated dermatology clinics in Oxford, which may have contributed to the early diagnosis and good outcome.

Regulation of epidermal growth factor receptor expression in human melanocytes

The epidermal growth factor receptor (EGFR) and its ligand, transforming growth factor alpha (TGFalpha), are reportedly involved in autocrine growth of melanoma cells. The signal pathway has also been implicated in early events of transformation, suggesting a function for EGFR in normal cells. This study reports the presence of EGFR in cultured melanocytes and examines some cellular responses to TGFalpha. Western analysis revealed 170 kDa bands in extracts of cultured neonatal human melanocytes, corresponding to the receptor Mr. Protein expression was more pronounced in cells during active growth. EGFR were less evident in cultures populated predominantly by melanized cells, indicating that receptor expression became reduced in differentiating cells. Immunocytochemistry confirmed these observations and also showed that EGFR reactivity was predominantly localized in the cell body but absent from dendrites. Addition of TGFalpha to early cultures induced a rapid increase in phosphotyrosine signal of the 170 kDa protein. Longer treatment (24-48 h) increased the intensity of the EGFR signal, suggesting that receptors had been upregulated. However, inclusion of TGFalpha in cultures did not result in an increase in cell numbers when compared to controls. The observations provide evidence of the existence of a receptor-mediated pathway in melanocytes which has transforming potential in vivo.

Overview of skin cancer detection and prevention for the primary care physician

The incidence of both melanoma and nonmelanoma skin cancer is increasing, and an accurate and timely diagnosis is important to reduce the morbidity and mortality associated with these malignancies. Clinical features and examination techniques are discussed, and the need to recognize important secondary tumor characteristics, which supplement the primary diagnosis, is reviewed. Recent evidence on etiologic factors and their importance are addressed to highlight the role of primary prevention. Pediatricians, family physicians, and all primary care physicians are encouraged to promote skin cancer awareness among children and their parents.

Excess of nevi related to immunodeficiency: a study in HIV-infected patients and renal transplant recipients

To assess the relationship between immune system and nevi, we studied two models of immunodeficiency caused by different mechanisms, i.e., virus and drug. Our rationale was that if an excess of nevi was found in these two epidemiologic models, it could be concluded that the excess was due to immunodeficiency itself rather than its cause. One hundred ten renal transplant recipients (RTR) were compared with age-, sex-, and phenotype-matched controls. Eighty four HIV-positive patients (HIV+) were compared with similarly matched controls. Nevi < 5 mm (N < 5) or > or = 5 mm (N > or = 5) were counted in three sites representative of regularly, intermittently, and never sun-exposed sites. The number of N < 5 was higher in RTR (p < 0.001) and in HIV+ (p < 0.001) than in respective controls. N > or = 5 were significantly higher only in RTR. These differences tended to be the same for all sites and persisted after adjustment for possible confounding factors. The incidence of atypical nevus was higher in RTR than in controls. Immunodeficiency seems to promote the occurrence of nevi. This supports the concept of immune surveillance of nevi and raises the question of whether sun-induced immune suppression plays a role in the development of nevi. As nevi are risk markers for melanoma, a higher incidence of melanoma could be expected in immunocompromised patients.

A new look at nevus-associated melanomas

The frequency with which malignant melanomas arise in association with preexisting melanocytic nevi has been studied extensively. We opted to evaluate new aspects of this association. In particular, we addressed the relative proportions of acquired versus congenital nevi involved and categorized the acquired nevi according to morphological type. Approximately 23% of the melanomas (29 of 124) in this group arose in association with preexisting nevi of which 55% (n = 16) were acquired and 28% (n = 8) were congenital (small). In 17% (n = 5) a distinction could not confidently be made. Of the acquired nevi, the vast majority were of Clark's type. It is clear that a relatively small proportion of melanomas as a whole are associated with preexisting nevi, and this number should be kept in perspective in devising strategies for early detection and prevention. The involvement of Clark's nevi in this regard is known, but to date the role of small congenital nevi has been underrecognized.

An overview of skin cancers. Incidence and causation

The incidence and mortality rates of skin cancer are rising in the United States and in many other countries. Concerns about stratospheric ozone depletion adding to the problem have made many organizations look at public and professional health programs as a possible solution. Early detection can reduce the problem in the short term, because mortality due to melanoma is clearly related to the depth of invasion of the tumor when it is removed. This is the factor which is amenable to change in an education program on early detection. Exposure to sunlight is clearly related to risk of development of skin cancer, including both melanoma and nonmelanoma skin cancers. This is the component of the equation of constitutional predisposition plus exposure to environmental risk factors leading to skin cancer that is amenable to change as a result of educational programs. On the basis of available data, there is a case for further development, provision, and evaluation of public and professional education programs designed to control what is becoming a major public health problem in the community.

A theory of site distribution of melanomas: Queensland, Australia

Although sun exposure is believed to be associated causally with cutaneous melanoma, the high incidence on less sun-exposed areas such as the back, as well as on chronically exposed sites such as the face, suggests that the association with sunlight is less straightforward than for other skin cancers. To explain this enigmatic site distribution, a theory of site-dependent susceptibility of melanocytes to malignant transformation is proposed. As possible evidence, all melanomas diagnosed in the state of Queensland, Australia, over a one-year period were surveyed for histologic evidence of benign melanocytic nevus cells adjacent to the melanoma, and analyzed according to anatomic distribution. Results showed a regional variation in the proportion of melanomas with adjacent nevi not explicable by regional variation in nevus density, which suggests that there is a varying susceptibility of nevi to malignant change. Given that nevus cells are equivalent to melanocytes, this finding would support the hypothesis that melanocytes at-large have a differential response to the mitogenic stimulus of sunlight according to anatomic site.