The report was concerned with the reasons why normal cells usually do not grow while in suspension, but do grow when they become attached to a substrate. Attachment causes growth in such cells in the sense that, given a requisite set of conditions, addition of the condition of attachment results in growth. Thus, growth would not occur but for attachment (but-for causality).
The authors showed that decreased activity of the cyclin E/CDK2 complex occurred in normal cells grown in suspension but not in transformed cells. They argued that because decreased activity of the CDK2 complex (due to increased levels of inhibitors) was associated with anchorage independence, the decreased activity could have caused the anchorage independence. The same reasoning was then applied to consideration of the causes of the decreased activity. The authors showed that increased concentration of CDK inhibitors and decreased phosphorylation of Thr160 occurred in association with the decreased activity, and concluded that one or both of these factors could have been the but-for cause of the decreased activity.