Classification of trophoblastic neoplasia.

A discussion of the classification of tro­ phoblastic neoplasms with clinical scien­ tists is of importance, for the work of those who direct pathology, biochemistry, en­ docrine and hematology laboratories is essential in the diagnosis and manage­ m ent of these neoplasms. Proper therapy requires the correct histopathologic diag­ nosis, monitoring of marrow, renal and marrow function and, m ost important, re­ liable m easurem ents of hum an chorionic gonadotropin (HCG). In addition to hav­ ing the responsibility for these, the clini­ cal scientist/pathologist is often called upon for information relative not only to p roper diagnosis bu t advice regarding proper treatm ent and prognosis. Trophoblastic neoplasia is a term which covers many different pathologic patterns as well as tumors beginning in several dif­ ferent organs. A useful classification is important not only for reporting results b u t also in helping establish the prognosis and proper treatm ent of individual pa­ tients. T he major division in trophoblastic n eo p las ia is in to those trophob lastic tumors which arise in placental tissue dur­ ing pregnancy (“ gestational” ) and those arising in ovary, testis or germ cell nests throughout the body (“non-gestational” ). This distinction is important for several reasons. In addition to differing in the tis ­ sue in which they arise, non-gestational trophoblastic tumors vary from gestational trophob lastic tum ors in th e ir c lin ica l course, response to chem otherapy and uniformity of HCG production. Because they arise in host tissue rather than fetal tissue, they lack the potential imm uno­ logic response based on differences in histocom patibility antigens which some investigators propose as the reason for the successful response of gestational tropho­ blastic neoplasms to chemotherapy. The trophoblastic elem ents in the non-gesta­ tiona l tum ors are alw ays m alig n an t whereas in the gestational variety there are both benign (hydatidiform mole) and m alignant forms (choriocarcinoma). F i­ nally, th e chorionic e lem en ts in nongestational tumors are often only one cell type in a tumor composed of other cell types. This is particularly true in tumors arising in the ovary or testis. For purposes of this presentation, only those tum ors arising in the chorionic epithelium lining the human placental villi will be discussed further.