Removing Spi or Egfr function in RasV12 clones (RasV12, spi_ or RasV12, Egfr_ double mutant cells) showed similar effects (Fig. 4b,c,e, and f), consistent with the notion that Egfr/Arf6 signalling stimulates Hh signalling in Ras tumours. The gene discussed is ARF6; the disease is neoplasm.