3 type of skin cancer

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Cancer, as a diagnosis, has frightening connotations to podiatric physicians, patients, and to the medical community. It is interesting to note, however, that a precise definition of the term "cancer" is elusive. Stedman's Medical Dictionary (24th edition) states that "cancer" is a general term used to designate a variety of malignant neoplasms. Such new growths (which are synonymous for neoplasia) invade surrounding tissues or spread to the many organs of the body and eventually cause death as these systems fail. Such cellular extensions(s) are designated as having metastasized. Recurrences are common after attempts at surgical removal.

One does not study human cancer in any depth before realizing that the foregoing definition is too simplistic. Verrucous carcinoma, for example, does not metastasize, nor does basal cell carcinoma or squamous cell carcinoma in situ. The statement just raised causes a need for additional explanation, which brings to mind fundamental embryology.

The fertilized ovum forms progressively into a ball-like configuration as the bastula and gastrula. Invaginations and evaginations develop as human form develops and three cellular layers are identified: An outer ectoderm (the prospective skin), an inner endoderm (the prospective gut), and a middle mesoderm from which bone, muscle and contiguous tissues eventually form.

A specialized region called the neural tube develops along a special region of ectoderm. This is mentioned as a special part of this brief discussion because melanocytes originate from neural crest cells. Poorly differentiated melanocytes produce the much feared skin tumor, melanoma. Carcinomas develop from ectodermal tissues and the sarcomas develop from tissues originally designated as mesodermal.

The present study of skin cancer is largely concerned with carcinomas, but even this statement requires some modification since some mesodermal tumors may erupt through the skin. Kaposi's sarcoma relates to regional superficial dermal blood vessels, usually in the lower extremities.

Histologic Anatomy

The histologic anatomy of "the skin" requires precise definition as cutaneous cancers are defined. The cellular layer above the dermis has been designated by some as the suprapapillary stratum Malpighi. (1) Downward well-organized bundles of the epidermis are the just mentioned papillae which normally extend perpendicular to the free surface of the skin into the dermis. The dermis, which underlies the cellular epidermis, is a mucopolysaccharide matrix in which blood vessels and nerves are plentiful. Eosinophils, basophyles, macrophages, melanocytes, melanophages, histiocytes and other cells can be observed microscopically wandering through the dermis. Their number and morphology are significant to pathologists, but the present study will be limited to the carcinomas of the cellular uppermost strata of the skin.

The dermis is, however, meaningful to skin cancer as the repository of the "dermal" influencing factor as defined by Vorhees and Duell. (2) "The Factors," presence in the dermis becomes relatively concentrated when epidermal cells are lost if wounds or normal sloughing of the skin occurs. This factor causes cells of the stratum basale and stratum spinosum to undergo mitosis in order to increase the cellular population of the epidermis proper and outermost stratum corneum.

Epidermis

The epidermis (or that cellular portion of the outermost skin covering which protects the innermost structures from a hostile environment) contains a substance (adenosine 3'5' monophosphate) which limits the amount of epidermal mitosis; so therefore, in the normal metabolism of "the skin" there exists an equipotential system which keeps the dermis and epidermis properly proportioned. This equilibration is clearly subject to change when pathology exists. The dermis and epidermis interface with a variety of configurations at the microscopically visible epidermal-dermal interface.

This region is not to be confused with the basement membrane, visible only with the electron microscope: that is a semipermeable membrane which can be construed as allowing biochemical information to be exchanged between dermis and epidermis. It becomes immediately clear as to the importance of such events when biochemical error is introduced into this otherwise balanced system.

In the nomenclature of skin cancer, it is important that the cellular structure of the epidermis is understood. Four strata or layers are classically stated. The stratum basale, the stratum spinosum, the stratum lucidum (understood by most to be an artifact of fixation occurring during tissue processing) the stratum granulosum and the outermost stratum corneum.

It now becomes important to identify the cellular layers of the skin, since tumors both benign and malignant are named relative to the cellular strata and we are about to discuss these entities.

Stratum Basale

The stratum basale is that layer of the skin positioned directly above the dermis. Such cells are slightly elongated and polarized at right angles to the free surface of the skin. The cells of the stratum basale are somewhat ovoid and have a dominant nucleus which is indicative of a propensity for biosynthetic activity and cell division. The basal cell nucleus does not usually demonstrate a well defined nucleolus. The cytoplasm of basal cell is relatively limited: the ratio of nucleus to cytoplasm is large-a phenomenon which will change as the basal cells undergo mitosis and proliferate upward toward the free surface of the skin.

The inductive influences of the dermis are increased by numerous papillae which interdigitate with fibrillar and matrix elements of the dermis. The mission of the stratum basale is to become active in the normal processes of keratinization, as evidenced by many free ribosomes, filaments, rough endoplasmic reticulum, and some mitochondria and golgi apparatus. The stratum basale, then, is a powerful reserve cell ready to replace cells lost from the free surface of the skin. Such cells may become involved in benign and malignant activity; neoplasia involving the basal cell (germinativum) is called basal cell carcinoma.

Basal cell carcinomas are not, however, limited to the more or less regular line demarcating dermis from epidermis. Many glands formed by invaginations and evaginations of the skin may also be involved in basal cell carcinoma; these include sebaceous glands. Hair follicles, hair shafts, and eccrine glands are all collectively called the adnexa. Basal cells may also exhibit unexpected activities such as motility and even phagocytosis in wound situations (as described by Ross and his co-workers)?

Stratum Spinosum