From this point on, melanoma is capable of spreading. The Breslows depth of the lesion is usually less than 1 mm (0.04 in), while the Clark level is usually 2. The vertical growth phase (VGP) following is invasive melanoma. The tumor becomes able to grow into the surrounding tissue and can spread around the body through blood or lymph vessels. The tumor thickness is usually more than 1 mm (0.04 in), and the tumor involves the deeper parts of the dermis. The host elicits an immunological reaction against the tumor during the VGP, which is judged by the presence and activity of the tumor infiltrating lymphocytes (TILs). These cells sometimes completely destroy the primary tumor; this is called regression, which is the latest stage of development. In certain cases, the primary tumor is completely destroyed and only the metastatic tumor is discovered. About 40% of human melanomas contain activating mutations affecting the structure of the B-Raf protein, resulting in constitutive signaling through the Raf to MAP kinase pathway.An insult common to most cancers is damage to DNA. UVA light mainly causes thymine dimers. UVA also produces reactive oxygen species and these inflict other DNA damage, primarily single-strand breaks, oxidized pyrimidines and the oxidized purine 8-oxoguanine (a mutagenic DNA change) at 1/10, 1/10, and 1/3rd the frequencies of UVA-induced thymine dimers, respectively. If unrepaired, CPD photoproducts can lead to mutations by inaccurate translesion synthesis during DNA replication or repair.
The Shope papilloma virus can cause rabbits to grow horns. This may have been the source of myths such as the Wolpertinger and the Jackalope. See also
Wart
Actinic keratosis
Epidermodysplasia verruciformis
List of cutaneous conditions

References
Further reading
Matthew Moore (2007-11-12). "Tree man who grew roots may be cured". London: Daily Telegraph. Archived from the original on 2007-11-13. Retrieved 2007-11-14. "Images of cutaneous horns". DermAtlas. Archived from the original on 2003-04-19. Retrieved 2007-11-14. DiClaudio, Dennis (2006) "The Hypochondriacs Pocket Guide to Horrible Diseases You Probably Already Have", Bloomsbury Publishing, ISBN 978-1-59691-061-4


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