Table 2. Separation of clusters of the NCI cell line panel obtained by the hierarchical cluster analysis shown in Figure 3 in comparison to drug sensitivity.

		Partitiona	Cluster 1	Cluster 2	Cluster 3	Chi2 Test
formulated arsenic trioxide	sensitive	≤−5.346	2	22	6
	resistant	>−5.346	20	10	0	3.32635×10−6
free arsenic trioxide	sensitive	≤−5.467	2	21	6
	resistant	>−5.467	20	10	0	4.50505×10−6

^aThe median log₁₀IC₅₀ value (M) for each drug was used as a cut-off to separate tumor cell lines as being "sensitive" or "resistant".