Fifty-two diagnostic studies were included (n=3,390 patient episodes). Seven centres provided 27 studies, but did not report the level of overlap between studies. The authors identified several factors that contributed to the clinical and methodological diversity of the evidence base and which made interpretation of the results of the studies difficult. These included:
Patient demographics: About half of the studies (25 studies) included only patients with colon cancer; other studies also included patients with rectal cancer, which were usually not reported as a subgroup and, therefore, contaminated the results. Not all studies reported mean age, gender distribution or basal metabolic index of patients.
Tumour profiles: Nineteen studies did not specifically exclude patients with distant metastases. Nine studies only included patients with clinically localised or resectable disease. Twenty-one studies resected fewer nodes per patient than the overall mean number of resected nodded (overall mean 15.3); 25 studies did not report the mean or range of the number of nodes resected. At least 21 studies included patients with T4 tumours and 25 studies had high T3 or T4 to T1 to T2 ratios.
Technical methodology: Only five studies ensured that surgeons were experienced in the technique at study baseline. Studies used relatively similar injection techniques, but differed in methods used for the histological analysis of identified nodes.
Only 15 studies analysed their false negative rates.
Only two studies (n=41 patients) specifically evaluated lymphatic mapping for early stage colon cancer.
Across all studies, there was considerable variation in detection rates (58% to 100%) and false negative rates (0% to 75%).
Studies with low diagnostic accuracy performance rates: Nine studies had detection rates of less than 90%. Thirty-two studies had false negative rates greater than 10%. Five studies with low detection rates had false negative rates greater than 20% (range 22% to 75%). Characteristics common among studies with detection rates less than 90% or false negative rates greater than 20% included: lack of reported validation of surgeons’ expertise; small sample size (n<60); inclusion of patients with rectal cancer; preponderance of T3/4 grade; and no critical analysis of the false negative rates.