During the development of a given organ or tissue within a multicellular organism, growth and patterning are controlled in a coordinated manner by the activity of a discrete number of signalling molecules and their corresponding pathways to give rise to a well-formed structure with a particular size, shape and pattern. Understanding how cells of different tissues or organs translate the activity of these pathways into an activation or repression of the cell cycle machinery in a context-dependent manner is at present one of the most intriguing questions in developmental and cancer biology. In this article we review the different roles of the Notch and Wingless signalling molecules in the regulation of cell cycle progression in the developing eye and wing imaginal discs of Drosophila and propose that, depending on how growth regulators are controlled in a context-dependent manner by the activity of these pathways, signalling molecules might have tumour suppressor or oncogene activity.