The present study examines symptom-based investigation of
lung and colorectal cancers from two points of view. First, it
provides estimates of the Symptom Lead Time (SLT) distribution
for these cancers. The SLT is the distribution of times between the
presentation of symptoms caused by cancer in primary care and the
eventual diagnosis of cancer (Lim et al, 2012; Ades et al, 2014). The
SLT’s role in a symptom-based programme is exactly analogous to
that of the Lead Time in a standard screening programme. In an
earlier, more technical, paper we estimated the SLT for lung cancer
taking account of the fact that a proportion of diagnoses are
already the result of GPs referring patients for chest X-ray (CXR)
following presentation of symptoms in primary care. We showed
that this had little impact on SLT. In this paper, we present
analyses of SLT for a wide range of potential investigational
criteria, in both lung and colorectal cancers.