In order to clarify the relationship between invasiveness and loss of cellular differentiation in tumor cells, we studied the invasive properties on Matrigel of (a) a series of clones we isolated from human neuroblastoma LaN1 and Platt cell lines inducible to differentiation by adhesion on fibronectin, and (b) SY5Y human neuroblastoma cells inducible to differentiation by retinoic acid. We found that, regardless of the parental line, the more differentiated clones were scarcely invasive, while the less differentiated clones showed a higher degree of invasiveness. Differences in invasiveness between differentiated and non-differentiated neuroblastoma clones did not reflect differences in adhesiveness to laminin, the major component of Matrigel. It is well known that tumor progression is associated with anaplasia, i.e., the morphological loss of several differentiative characteristics of the tumor's tissue of origin (Cotran et al., 1989). However, the relationship between anaplasia and formation of metastases, the hallmark of malignancy, has attracted little attention, and the few experimental studies in this area gave contradictory results. Eccles (1983) found an inverse correlation between histological differentiation and the capacity to metastasize in a series of transplantable murine mammary carcinomas and squamous-cell carcinomas. Moreover, a lower degree of differentiation paralleled the emergence of a metastatic phenotype in a series of murine melanoma cell lines submitted to serial passages in vivo and in vitro (Hearing et al., 1988). Gabbert (1989) reported that the morphological characteristics of the tissue of origin were maintained in the inner parts of rat and human carcinomas, but lost at the invasive edges. On the other hand, Bennett et al. (1994) and Prezioso et al. (1993) noted a positive correlation between differentiation and metastatic potential for sub-lines of the B16 murine melanoma.In order to study the relationship between differentiation and invasiveness, we investigated whether the differentiative characteristics of different systems of neuroblastoma lines correlate with their capacities of invading a reconstituted basement membrane (Matrigel). In this type of investigation, neuroblastoma cells represent a particularly useful model, since differentiation, easily assayed on the basis of neurite emission, may be induced under well-controlled conditions, such as treatment with appropriate pharmacological agents (Abemayor and Sidell, 1989), and adhesion to matrix-adhesive proteins, e.g., fibronectin (Waite et al., 1987; Mugnai et al., 1988a,b;Arcangeli et al., 1993), vitronectin (Arcangeli et al., 1993 and laminin (Rossino et al., 1991).The systems of neuroblastoma cells used in our study were represented by (a) a series of clones that we isolated from human neuroblastoma LaN1 and Platt cell lines by the limiting dilution technique, and (b) the SY5Y human neuroblastoma cell line. The LaN1 and Platt lines differentiate upon adhesion to fibronectincoated substrata (Waite et al., 1987), while ...