= Dermatopathology
\b[Dermatopathology] studies disease in sampled <skin> and its appendages through tissue structure, cellular appearance and the clinical context. It connects <dermatology> with <histology>: a visible lesion and a thin <histological section> of that lesion are different observations of the same biological process.
A <skin biopsy> provides a specimen rather than an automatic diagnosis. The interpretation depends on which part was sampled, how its structures are represented in the section and which biological question is being asked. <Clinicopathological correlation> relates the microscopic findings to the lesion's location, appearance and course. The American Academy of Dermatology describes the <dermatopathologist>'s role in examining biopsy tissue and preparing a pathology report.<What is a dermatologist? by the American Academy of Dermatology>[Dermatopathologist subsection, tissue examination and report]{ref}
Sampling geometry illustrates a limitation. In an original spherical-lesion model with radius $R$, a planar section a distance $z$ from the centre has apparent radius
$$
r(z)=\sqrt{R^2-z^2},\qquad |z|\le R.
$$
For $R=1\,\mathrm{mm}$, a central section shows diameter $2\,\mathrm{mm}$, whereas a section at $z=0.8\,\mathrm{mm}$ shows $1.2\,\mathrm{mm}$. A smaller profile does not establish that the original three-dimensional structure was smaller. This chosen geometry is explanatory, not a model for classifying a particular lesion.
Interpretation is itself testable. A primary observer study used 240 skin-biopsy cases assigned in sets for repeated interpretation at least eight months apart; 187 pathologists participated in its first phase. It evaluated <diagnostic reproducibility> and agreement with a consensus reference for <melanocytic lesions>.<Pathologists' diagnosis of invasive melanoma and melanocytic proliferations: observer accuracy and reproducibility study by Joann G. Elmore and others>[Abstract, Design, Participants and Outcomes]{ref} Repeating classification separates within-observer consistency, between-observer variation and agreement with the defined reference.
These are distinct questions. Tissue processing and optical observation concern what evidence is available; classification concerns how that evidence is interpreted. A reproducible label need not answer every clinical question, and a consensus reference is an explicitly constructed comparator rather than direct access to every aspect of biological truth.
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