Factors of importance for scintigraphic non-visualisation of sentinel nodes in breast cancer

The aim of this study was to analyse different factors of possible significance for non-visualisation of sentinel nodes (SNs) by preoperative lymphoscintigraphy, in order to enable improvement of the success rate of SN visualisation through modification or alteration of some of the factors.

Between March 1998 and January 2003 we analysed a series of 442 women with unilateral stage T1 and clinical N0 breast cancer. Lymphoscintigraphy was performed after periareolar or peritumoural injection of 99mTc-albumin nanocolloid, with image acquisition after 2-6 h or 18-24 h. Until January 2001, all patients received around 20 MBq tracer, irrespective of time to operation. From January 2001, patients injected on the day before surgery received at least 100 MBq while patients injected on the day of surgery received around 50 MBq.

An SN was visualised in 87% of the patients, and at surgery the SN was detected with the hand-held gamma probe in 42% of the remaining patients. By multiple logistic regression analysis, statistically significant independent variables that increased the risk for non-visualisation were increasing age (p=0.0007), increasing body weight (p=0.0189) and peritumoural injection (p<0.0001). Significant interaction was found for imaging time and injected activity (p=0.0017).

This study conclusively shows that the risk of unsuccessful SN imaging increases with age and body weight. Our findings suggest that the scintigraphic success rate may be improved by periareolar (rather than peritumoural) injection. Early and late imaging procedures are equally efficient, but if a late imaging procedure is used, activity (adjusted for physical decay) in the patient on day 2 should be more than 10 MBq.