The growth patterns of established normal and cancer cell lines, cultured i
n monolayer and collagen gel, have been characterized using the cluster siz
e distribution of cellular aggregates. HN-5 (cancer) cells exhibit, either
in gel or in monolayer, power-law distributions at any time in culture, whe
reas for MDCK ("normal") and Hep-2 (cancer) cells there is a transition fro
m an exponential behavior to a power-law distribution after a transient tim
e in culture. These results suggest that the transitions in growth regimes
observed in MDCK and Hep-2 cell lines might be associated to changes in the
control of replication or in the expression patterns of cell adhesion mole
cules of cell-cell and cell-matrix type related to intracellular signalling
. These transitions are irreversible and seems to be an adaptative response
to the growth constraints imposed by high cell population density or long
permanence in culture. (C) 2001 Elsevier Science B.V. All rights reserved.