Invasiveness in vitro of two mammary adenocarcinoma tumors with different metastasizing ability

The adhesive and invasive capacities of a transplantable mammary adenocarcinoma that grew spontaneously in a BALB/c mouse with a moderate lung metastatic ability (M3) and a related variant tumor with a higher metastatic potential (MM3) were confronted with precultivated fragments of neonatal syngeneic lung and kidney in three-dimensional culture. M3 cells adhered only to lung as isolated clusters or surrounded the fragments, forming a dense rim. These adherent cells invaded half of the lung pieces in few places and as thick tongues. On the other side, the highly metastatic tumor MM3 adhered to lung and kidney with a similar frequency, mostly surrounding the confronted fragments as a monolayer. MM3 cells deeply infiltrated the lung and kidney pieces, at several points up to 70 and 100%, respectively, either as fine strands or as solitary cells. Invasion by MM3 cells was always accompanied by a dense, homogeneous, acidophilic necrosis of the whole fragments. The higher in vitro invasiveness of MM3 cells could be associated to their higher metastasizing potential in vivo.