BACKGROUND: Cancer survival in Spearhead Primary Care trusts (PCTs) is lower than in the rest of England for most common cancers, but differences are smaller than the more substantial survival gradients between deprived and affluent populations using small-area measures of deprivation. The way in which Spearhead PCTs were designated may give an unduly favourable image of inequalities in cancer survival. METHODS: Five-year age-standardised relative survival for 10 common cancers was estimated separately for patients resident in Spearhead local authorities (LAs), Spearhead PCTs, and the rest of England. Differences in survival between Spearhead and other LAs and the corresponding differences between Spearhead and other PCTs were compared. RESULTS: Cancer survival was consistently lower for patients resident in Spearhead areas than in the rest of England for the majority of cancers, regardless of the geographic unit used. Survival was lower in Spearhead LAs than Spearhead PCTs for 11 of the 16 cancer-sex combinations examined. As a consequence, the survival gap between the Spearhead areas and the rest of England was slightly wider when the definition of Spearhead was based on LAs rather than PCTs, but the two contrasts provide a very similar picture. CONCLUSIONS: Small differences were found between using Spearhead LAs and Spearhead PCTs in the estimation of cancer survival, but results were inconsistent. Although the overlap between the two geographies is imperfect, Spearhead PCTs are appropriate geographic units for monitoring inequalities in cancer survival. However, given the instability of NHS geographical boundaries, Spearhead LAs could be a suitable alternative geographic unit.