Divergency between incidence of microscopic and macroscopic metastases.

In a rat fibrosarcoma model (D-12), the incidence of macroscopic metastases was generally low but critically dependent on the site of the primary tumor implant; surgical removal of the primary tumor either induced or markedly enhanced the outgrowth of macroscopic metastases (Keller 1981). The present histological and biological findings indicate that dissemination of neoplastic cells and colonization of draining lymph nodes is a spontaneous, early occurring and continuing process. The incidence of micrometastases within lymph nodes by far exceeded the incidence of macroscopically evident metastases. Other evidence suggests that the growth characteristics of D-12 tumor cells derived from metastases are not measurably different from D-12 cells inducing primary tumor growth.