Activity of a cellular signaling pathway in tissue of a medical subject is inferred based at least on expression levels of target genes of the cellular signaling pathway measured in an extracted sample of the tissue of the medical subject. It is determined whether the cellular signaling pathway is operating abnormally in the tissue of the medical subject based on the inferred activity of the cellular signaling pathway. The inferring is suitably performed by a digital processing device using a probabilistic model of the cellular signaling pathway, such as a Bayesian network model. The cellular signaling pathway may be a Wnt pathway for which the target genes are suitably selected from the group: KIAA1199, AXIN2, CD44, RNF43, MYC, TBX3, TDGF1, SOX9, ASCL2, IL8, SP5, ZNRF3, EPHB2, LGR5, EPHB3, KLF6, CCND1, DEFA6, FZD7, NKD1, OAT, FAT1, LEF1, GLUL, REG1B, TCF7L2, COL18A1, BMP7, SLC1A2, ADRA2C, PPARG, DKK1, HNF1A, and LECT2.
