= Melanocytic lesion
A melanocytic lesion is a localized abnormal growth or proliferation involving <melanocytes>, the pigment-producing <biological cells> of the <skin>. The description identifies the participating cell lineage; it does not by itself mean cancer. A common <melanocytic nevus> is a noncancerous clustered growth of <melanocytes>, whereas <melanoma> is malignant. The National Cancer Institute distinguishes these categories explicitly.<Common Moles, Dysplastic Nevi, and Risk of Melanoma by the National Cancer Institute>[What is a common mole? and Can a common mole turn into melanoma?]{ref}
A visible pigmented spot and a <histological section> provide different evidence. Pigment is an optical observation; a melanocytic lesion is a statement about the biological process. Microscopic examination asks how <melanocytes> are arranged in the sampled <tissue> and how that pattern relates to surrounding structures. <Clinicopathological correlation> connects those observations to the particular lesion that was sampled.
The sampling distinction can be made quantitative without inventing a diagnostic rule. In a constructed lesion containing $N$ relevant cells, examining a section that contains $n$ cells does not automatically inspect all $N$. If a feature is absent from the section, it may be absent from the lesion or located outside the sampled region. Increasing the number of levels or changing the sampled location changes the evidence available, rather than merely changing the name assigned to it.
Classification is also an observer task. A primary study of <skin biopsy> interpretations included a spectrum from nevi to invasive <melanoma> and distinguished agreement with a consensus reference from agreement on repeat interpretation.<Pathologists' diagnosis of invasive melanoma and melanocytic proliferations: observer accuracy and reproducibility study by Joann G. Elmore and others>[Abstract, five diagnostic classes and observer/reference comparison]{ref} This motivates precise statements of the category, sampled material and <diagnostic reproducibility>. A lineage label alone does not specify benignity, invasiveness or a complete clinical diagnosis.
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