The most common, in a given day's work, are:
- Squamous cell carcinoma (including solar [actinic] keratoses; a malignant
epithelial neoplasm)
- Basal cell carcinoma (also known as trichoblastic
carcinoma, a malignant epithelial neoplasm)
- Seborrheic Keratosis (a benign
epithelial neoplasm)
- Keratoacanthoma (a kind of epithelial hyperplasia that
often simulates squamous cell carcinoma)
- Wart or verruca or condyloma (a
kind of epithelial hyperplasia caused by human papillomavirus infection)
- Cysts
- Melanocytic nevus (a benign proliferation of melanocytes - some are
hamartomas; others are benign neoplasms)
- Melanoma (a malignant
proliferation of melanocytes, which is a type of sarcoma)
- Psoriasis (a kind of genodermatosis)
- Spongiotic dermatitis (referred
to often as "eczema", which is an imprecise way to refer to specific diseases
that manifest themselves histologically as spongiosis)
- Hypersensitivity
reactions (inflammatory reactions caused by a sensitizing agent)
- Allergic
reactions (inflammatory)
- Infections (the cause is known, an organism, but the result is usually an
inflammatory response in the skin)
- Lupus erythematosus (an autoimmune
disorder that often manifests as an inflammatory pattern in the skin)
Broadly, with some clarifications, all diseases of skin are dermatoses,
which means, simply, "a disease of the skin". Yet, most dermatopathologists
separate skin diseases into three main categories:
1. Inflammatory Diseases (including autoimmune disease and infectious
disease)
2. Simulators of Inflammatory Diseases (including metabolic
diseases)
3. Non-inflammatory cellular proliferations (including
neoplasms and some simulators of inflammatory disease).
It is not completely accurate to attribute the term "neoplasm" to all
non-inflammatory cellular proliferations. A neoplasm means a "new growth", in
contrast with, for instance, an abnormal proliferation of cells identified at or
near birth that simulates the normal tissue at the given location, but is
positioned abnormally (hamartoma). All lesions that present clinically as
tumors (i.e., papules, nodules, and larger masses) are not neoplasms. As a
rule, they are divided into the following categories:
1. Malformation (congenital, benign)
2. Cyst
3. Hyperplasia (stimulus dependent, benign)
4. Hamartoma (congenital
or tardive, benign)
5. Neoplasm (both stimulus independent, benign &
malignant)
As a rule, neoplasms are divided into epithelial (from cells lining
surfaces or ducts) and parenchymal (everything else, including supporting
stroma, blood vessels, neural tissue, melanocytes etc). Malignant epithelial
neoplasms are termed "carcinomas", while malignant non-epithelial neoplasms are
termed "sarcomas".