Pathology Terminology

 

 

Neoplasia

Neoplasia literally means the process of "new growth," and a new growth is called a neoplasm. The term tumor was originally applied to the swelling caused by inflammation. Neoplasms also may induce swellings, but by long precedent, the non-neoplastic usage of tumor has passed into limbo; thus, the term is now equated with neoplasm.  Although all physicians know what they mean when they use the term neoplasm, it has been surprisingly difficult to develop an accurate definition. The eminent British oncologist Willis[5] has come closest: "A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues and persists in the same excessive manner after cessation of the stimuli which evoked the change."

 

 

Dysplasia

dysplasia, a term that literally means disordered growth. Dysplasia is encountered principally in epithelia, and it is characterized by a constellation of changes that include a loss in the uniformity of the individual cells as well as a loss in their architectural orientation. Dysplastic cells also exhibit considerable pleomorphism and often contain hyperchromatic nuclei that are abnormally large for the size of the cell. Mitotic figures are more abundant than usual, although almost invariably they conform to normal patterns. Frequently the mitoses appear in abnormal locations within the epithelium. Thus, in dysplastic stratified squamous epithelium, mitoses are not confined to the basal layers and may appear at all levels and even in surface cells. The architecture of the tissue may be disorderly. For example, the usual progressive maturation of tall cells in the basal layer to flattened squames on the surface may be lost and replaced by a scrambling of dark basal-appearing cells throughout the epithelium. When dysplastic changes are marked and involve the entire thickness of the epithelium, but the lesion remains confined to the normal tissue, it is considered a preinvasive neoplasm and is referred to as carcinoma in situ.

Figure 7-11 A, Carcinoma in situ. This low-power view shows that the entire thickness of the epithelium is replaced by atypical dysplastic cells.

 

 

 

 

Adenoma

Adenoma is the term applied to a benign epithelial neoplasm that forms glandular patterns as well as to tumors derived from glands but not necessarily reproducing glandular patterns. On this basis, a benign epithelial neoplasm that arises from renal tubular cells growing in the form of numerous tightly clustered small glands would be termed an adenoma, as would a heterogeneous mass of adrenal cortical cells growing in no distinctive pattern.

 

 

Polyp:

When a neoplasm, benign or malignant, produces a macroscopically visible projection above a mucosal surface and projects, for example, into the gastric or colonic lumen, it is termed a polyp The term polyp is preferably restricted to benign tumors. Malignant polyps are better designated polypoid cancers.

Figure 7-2 Colonic polyp. A, This benign glandular tumor (adenoma) is projecting into the colonic lumen and is attached to the mucosa by a distinct stalk. B, Gross appearance of several colonic polyps.

 

Differentiation and Anaplasia

Differentiation refers to the extent to which neoplastic cells resemble comparable normal cells, both morphologically and functionally; lack of differentiation is called anaplasia. Well-differentiated tumors are composed of cells resembling the mature normal cells of the tissue of origin of the neoplasm. Poorly differentiated or undifferentiated tumors have primitive-appearing, unspecialized cells. In general, benign tumors are well differentiated.  The neoplastic cell in a benign smooth muscle tumor—a leiomyoma—so closely resembles the normal cell that it may be impossible to recognize it as a tumor by microscopic examination of individual cells. Only the massing of these cells into a nodule discloses the neoplastic nature of the lesion.

Malignant neoplasms, in contrast, range from well differentiated to undifferentiated. Malignant neoplasms composed of undifferentiated cells are said to be anaplastic. Lack of differentiation, or anaplasia, is considered a hallmark of malignant transformation. Anaplasia literally means "to form backward," implying a reversion from a high level of differentiation to a lower level. There is substantial evidence, however, that most cancers do not represent "reverse differentiation" of mature normal cells but, in fact, arise from stem cells that are present in all specialized tissues. The well-differentiated cancer evolves from maturation or specialization of undifferentiated cells as they proliferate, whereas the undifferentiated malignant tumor derives from proliferation without complete maturation of the transformed cells.

 

 

 

Carcinoma

Malignant (tending to infiltrate, metastasize, and terminate fatally)  neoplasms of epithelial cell origin, derived from any of the three germ layers, are called carcinomas. Thus, cancer arising in the epidermis of ectodermal origin is a carcinoma, as is a cancer arising in the mesodermally derived cells of the renal tubules and the endodermally derived cells of the lining of the gastrointestinal tract.

 

 

 

Adenocarcinoma

Carcinomas may be further qualified. One with a glandular growth pattern microscopically is termed an adenocarcinoma.

Figure 7-7 Malignant tumor (adenocarcinoma) of the colon. Note that compared with the well-formed and normal-looking glands characteristic of a benign tumor, the cancerous glands are irregular in shape and size and do not resemble the normal colonic glands. This tumor is considered differentiated because gland formation can be seen. The malignant glands have invaded the muscular layer of the colon.

 

 

 

 

TABLE 7-1 -- Nomenclature of Tumors

Tissue of Origin

Benign

Malignant

Composed of One Parenchymal Cell Type

 

 

Tumors of mesenchymal origin

 

 

Connective tissue and derivatives  

Fibroma

Fibrosarcoma

 

Lipoma

Liposarcoma

 

Chondroma

Chondrosarcoma

 

Osteoma

Osteogenic sarcoma

Endothelial and related tissues

 

 

Blood vessels  

Hemangioma

Angiosarcoma

Lymph vessels  

Lymphangioma

Lymphangiosarcoma

Synovium  

 

Synovial sarcoma

Mesothelium  

 

Mesothelioma

Brain coverings  

Meningioma

Invasive meningioma

Blood cells and related cells

 

 

Hematopoietic cells  

 

Leukemias

Lymphoid tissue  

 

Lymphomas

Muscle

 

 

Smooth  

Leiomyoma

Leiomyosarcoma

Striated  

Rhabdomyoma

Rhabdomyosarcoma

Tumors of epithelial origin

 

 

Stratified squamous  

Squamous cell papilloma

Squamous cell or epidermoid carcinoma

Basal cells of skin or adnexa  

 

Basal cell carcinoma

Epithelial lining of glands or ducts  

Adenoma

Adenocarcinoma

 

Papilloma

Papillary carcinomas

 

Cystadenoma

Cystadenocarcinoma

Respiratory passages  

Bronchial adenoma

Bronchogenic carcinoma

Renal epithelium  

Renal tubular adenoma

Renal cell carcinoma

Liver cells  

Liver cell adenoma

Hepatocellular carcinoma

Urinary tract epithelium (transitional)  

Transitional cell papilloma

Transitional cell carcinoma

Placental epithelium  

Hydatidiform mole

Choriocarcinoma

Testicular epithelium (germ cells)  

 

Seminoma

 

 

Embryonal carcinoma

Tumors of melanocytes

Nevus

Malignant melanoma

More Than One Neoplastic Cell Type—Mixed Tumors, Usually Derived from One Germ Cell Layer

 

 

Salivary glands

Pleomorphic adenoma (mixed tumor of salivary origin)

Malignant mixed tumor of salivary gland origin

Renal anlage

 

Wilms tumor

More Than One Neoplastic Cell Type Derived from More Than One Germ Cell Layer—Teratogenous

 

 

Totipotential cells in gonads or in embryonic rests

Mature teratoma, dermoid cyst

Immature teratoma, teratocarcinoma