Elevation of cGMP concentration, as a result of defects and/or aberrant expression of photoreceptor specific PDE6, leads to hyper-activation of PKG isoforms, which in turn contributes to the progression of malignant melanoma in skin and breast cancer cells [7,39] and various kinds of cancer pathologies in lungs, stomach, endometrium and as well as in familial retinitis pigmentosa [14,16,23,32,55]. This evidence concerns the gene PRKG1 and melanoma.