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In their recent paper on small cell malignant melanoma,1 Blessing and co-workers report a series of 15 melanocytic lesions that, on the basis of their histology, were considered to constitute a new variant of naevoid melanoma—melanoma resembling naevus.
I am concerned about the lack of metastases in the reported series. Only documentation of metastasis constitutes formal proof that the lesions are diagnosed correctly as melanomas; histological resemblance to some features of melanoma by itself can never provide the necessary conclusive evidence. In addition, I cannot agree with the authors that some of the features of these lesions—such as vascular proliferation, lymphocytic infiltrate, and lentiginous junctional component—constitute supportive evidence of malignancy. Furthermore, the authors point out that in some respects the lesions resembled benign naevi; it is unclear why the resemblance to melanoma would be more relevant than the resemblance to naevus. From the illustrations provided in the paper, I am not sure that I would issue a confident diagnosis of melanoma.
One needs to have more cases with follow up to obtain a better picture of the possible malignant potential of these lesions. If no metastases are encountered in an expanded series, then the message of the paper would be very different and similar to the one of Sophie Spitz in her classic paper on what was then termed juvenile melanoma2: the lesions under study resemble melanoma in some respects, but are devoid of malignant potential. Careful correlation of histology with follow up data in a large series is the only way to solve this issue and to know how to interpret such lesions correctly.
The authors reply
We would like to thank Professor Mooi for taking an interest in our recent article describing small cell melanoma as a variant of classic melanoma.1 The points that he makes are of course entirely relevant and are, we feel, generally covered in the manuscript; indeed, the title reflects the fact that the diagnosis might be contentious. Therefore, only the main points of his letter will be discussed.
He rightly comments that there is a lack of metastases in our cases. However, apart from one lesion that measured 1.1 mm, all were less than 1.0 mm, with a mean of 0.63 mm, and therefore the clinical behaviour of these cases is not unexpected. It is of course possible that “small cell melanoma” may have an inherently less aggressive behaviour. In addition, although we accept that metastasis is the gold standard for the diagnosis of malignancy, histopathologists readily accept basal cell carcinoma as a malignant epithelial neoplasm without metastatic potential and, indeed, those who accept the concept of the radial growth phase in melanoma are quite happy to call these potentially non-metastasising lesions melanomas.
Professor Mooi expresses discontent over the features such as lentiginous junctional growth pattern, lymphohistiocytic infiltrate, and vascular proliferation as being supportive of malignancy. We agree that no feature in isolation is indicative of malignancy and that all features, clinical and histopathological, should be taken into account before reaching a diagnosis. However, two of these features are cited by major texts, and a lentiginous melanocytic growth pattern in an older patient (mean age, 48.6 years) in the absence of trauma is in our opinion supportive of at least in situ disease. The relative importance placed on these features may depend on whether one accepts the entity of dysplastic naevus, and here also we have a controversial entity with the problem of lack of reproducible histological features and disagreement over whether the lesion, if it exists, is a precursor to or risk marker of subsequent melanoma.
Melanocytic lesions comprise a heterogeneous group in which the biological behaviour of some of the more common entities is clearly understood. However, we believe it is essential for the less common entities (such as small cell melanoma) to be recognised and grouped with similar lesions so that accurate conclusions regarding their biological behaviour can be made; unless the entity that we have labelled “small cell melanoma” is clearly defined we will never collect the long term follow up data that will enable an assessment of its true biological potential. Until then, it is important that we all keep an open mind and in the words of the English philosopher Bertrand Russell who on being asked if he would be willing to die for his beliefs replied: “Of course not. After all, I may be wrong.”.2
If “small cell melanoma” is the next Spitz naevus that's OK by us.