Choristoma is a congenital anomaly consisting of a heterotopic nest of cells. For example, a small nodule of well-developed and normally organized pancreatic tissue may be found in the submucosa of the stomach, duodenum, or small intestine. The designation -oma, connoting a neoplasm, imparts to these lesions an undeserved gravity, as they are usually of trivial significance.
Although the terminology of neoplasms is regrettably complex, an understanding of the nomenclature is important because it is the language by which a tumor’s nature and significance is communicated among physicians in different disciplines involved in cancer care.
Fig. 6.2 Mixedtumoroftheparotidgland.Smallnestsofepithelialcellsandmyxoidstromaformingcartilageandbone(anunusualfeature)arepresentinthisfield.(Courtesy of Dr. Vicky Jo, Department of Pathology, Brigham and Women’s Hospital, Boston, Massachusetts.) http://ebooksmedicine.net
More Than One Neoplastic Cell Type—Mixed Tumors, Usually Derived From One Germ Cell Layer
TotipotentialcellsingonadsorinembryonicMatureteratoma,dermoidcystImmatureteratoma,teratocarcinomarests
There are three fundamental features by which most benign and malignant tumors can be distinguished: differentiation and anaplasia, local invasion, and metastasis. In general, rapid growth also signifies malignancy, but many malignant tumors grow slowly and as a result growth rate is not a reliable discriminator between good and bad actors. Nothing is more important to the patient with a tumor than being told: “It is benign.” Although some neoplasms defy easy characterization, in most instances the determination of benign versus malignant is made with remarkable accuracy using long-established clinical and anatomic criteria.
Differentiation refers to the extent to which neoplasms resemble their parenchymal cells of origin, both morphologically and functionally; lack of differentiation is called anaplasia. In general, benign neoplasms are composed of well-differentiated cells that closely resemble their normal counterparts. A lipoma is made up of mature fat cells laden with cytoplasmic lipid vacuoles, and a chondroma is made up of mature cartilage cells that synthesize their usual cartilaginous matrix—evidence of morphologic and functional differentiation. In well-differentiated benign tumors, mitoses are usually rare and are of normal configuration.
By contrast, while malignant neoplasms exhibit a wide range of parenchymal cell differentiation, most exhibit morphologic alterations that betray their malignant nature.
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Fig. 6.3 Well-differentiatedsquamouscellcarcinomaoftheskin.Thetumorcellsarestrikinglysimilartonormalsquamousepithelialcells,withintercellularbridgesandnestsofkeratin(arrow). (Courtesy of Dr.Trace Worrell,Department of Pathology, University of Texas Southwestern Medical School, Dallas,Texas.)
In well-differentiated cancers, these features may be quite subtle (
Fig. 6.3 ). For example, well-differentiated adenocarcinoma of the thyroid gland may contain normal-appearing follicles, its malignant potential being only revealed by invasion into adjacent tissues or metastasis. The stroma carrying the blood supply is crucial to the growth of tumors but does not aid in the separation of benign from malignant ones. The amount of stromal connective tissue does, however, determine the consistency of a neoplasm. Certain cancers induce a dense, abundant fibrous stroma (desmoplasia), making them hard, so-called “scirrhous tumors”.