Table 1: Hypothetical Two-step Model of “Initiation” in the Process of Experimental Carcinogenesis by PAHs (skin) and AZOs (Liver)

Step 1	Step 2	Step 3	Step 4	Result
-------	INITIATION B	CONVERSION	PROMOTION	No Tumors
INITIATION A	-------	CONVERSION	PROMOTION	Nonautonomous Tumors: Papillomas (skin) Nodules (liver)	Regression
INITIATION A	INITIATION B	CONVERSION	PROMOTION	Persistent Tumors	Progression → CANCER
Complete Initiation		Complete Promotion
INITIATION A: Point mutations by “ultimate carcinogens” and hence also the activation of proto-oncogenes to oncogenes [9]. Result: Among other things, the activation of oncogenes whose products are active at the plasma membrane. INITIATION B: Formation of PAH/cholesterol/apoA-I - or AZO/cholesterol/apoA-I complexes in the plasma membrane [3, 4]. Result: Reversible changes in the membrane architecture and its functions. Hypothesis: INITIATION A can co-operate with INITIATION B at the plasma membrane. See text. Result: An irreversibly modified membrane architecture with negative consequences for growth control. CONVERSION and PROMOTION see: Marks and Frstenberger [1]; Schwarz [2].