Gross and Microscopic Pathology and Pathophysiology Part II Marc D. Brown, M.D. and Glynis A. Scott M.D.

SKIN TUMORS

Cutaneous Tumors

Tumors arising from epidermis

Premalignant epidermal tumors
	Actinic keratoses Also termed senile or solar keratoses Arise on sun exposed skin usually in older individuals. Appears as a red, rough, flat papule Skin usually shows evidence of chronic sun damage. Actinic keratoses may evolve eventually into squamous cell carcinomas. Histology: Analogous to dysplasia seen in the uterine cervix. There is atypia of the basal to mid-level keratinocytes (high N/C ratio, mitotic figures), parakeratin (giving a scaly appearance), and solar elastosis in the dermis.
	Bowen's disease Squamous cell carcinoma in situ. Most common in men with fair complexions arising in actinically damaged skin; usually appearing erythematous, rough surfaced and scaling. Bowen's disease may occur on mucosal surfaces such as the glans penis. Histology: Full thickness dysplasia of the keratinocytes with numerous large atypical cells with bizarre mitoses.
Malignant epidermal tumors
	Basal cell carcinoma Histology: of Basal cell carcinoma (BCC): Characterized by a proliferation of basaloid cells which resemble the cells lining the basal epidermis. These cell grow in groups and strands into the dermis.
	Squamous cell carcinoma   Histology: of Squamous cell carcinoma (SCC): Characterized by malignant squamous cells that arise from the epidermis. They retain the ability to make keratin so a common feature of SCC is the presence of keratin "pearls" in the dermis.

Tumors of Melanocyte System: a review

	Common nevi Moles are the most common tumors. These benign pigmented lesions arise from the melanocyte and are categorized into 3 groups depending upon the location of the nevus cells (junctional, compound, intradermal). Junctional nevi are usually flat and deeply pigmented. Intradermal nevi can be nonpigmented with a dome shaped appearance.
	Congenital nevi By definition, congenital nevi are present at birth. They usually remain throughout life. Most congenital nevi are small but a small percentage are very large and are referred to as giant congenital nevi. Many congenital. nevi have associated overgrowth of hairs. Controversy surrounds the risk of malignant transformation of congenital nevi. Large congenital nevi have a significant risk of developing melanoma (5-15%) before puberty whereas in small congenital nevi this risk is probably less than 1%.
	Halo nevi These are ordinary appearing nevi that develop a depigmented halo around them. Occasionally the central nevus will regress.
	Blue nevus This is a blue black nodule with a smooth surface. The deep pigmentation is due to large amounts of melanin pigment within the deeper dermis.
	Dysplastic nevi Dysplastic nevi are moles that appear atypical both clinically and histologically. In some individuals, dysplastic nevi serve as markers for the development of malignant melanoma. We worry most about dysplastic nevi in patients where there is a family history of melanoma. Also, the greater the number of dysplastic nevi the greater the risk of malignant transformation. Patients with dysplastic nevi but no family history are said to have sporadic dysplastic nevus syndrome and here the risk for melanoma is much less significant. In general, dysplastic nevi tend to occur in much greater numbers than ordinary nevi and patients frequently have 100 or more lesions. These nevi are often larger with irregular margins and irregular pigmentation. Although ordinary moles have usually stopped appearing by early adult life, dysplastic nevi may continue to develop into the adult years.
	Lentigo Patients with fair skin and a history of sun exposure will develop solar lentigines usually during their SO's & 60's. These are sometimes referred to as "liver spots" or "old age spots". The lesions are confined to sun exposed areas, very common on the face and the dorsal surface of the hands.

Histology of Benign Melanocytic lesions:
Nevi are composed of groups of nevic cells (modified melanocytes) present in the epidermis (Junctional nevi), dermis (dermal nevi) or both (compound nevi). A benign nevus, in contrast with malignant melanoma cells, is small, does not show much (if any) mitotic activity, and is well circumscribed. Dysplastic nevi show histologic evidence of progression to malignancy: asymmetry, large atypical nevic cells, and evidence of an inflammatory reaction. A lentigo is not really a nevus; it is a proliferation of single melanocytes at the dermal-epidermal junction. Nevi are characterized by groups of specialized melanocytes (nevic cells).

Malignant melanoma

	Superficial spreading
	Nodular
	Lentigo malignant melanoma
	Acral

Histology of Malignant Melanoma (MM):
The sina qua non of MM is the presence of large atypical melanocytes either confined to the epidermis (MM-in -situ) or infiltrating into the dermis (MM).Malignant melanocytes show "Pagetoid spread" of cells upward in the epidermis as a characteristic feature.