Computer simulations of lymph node metastasis for optimizing the pathologic examination of sentinel lymph nodes in patients with breast carcinoma

BackgroundMany empiric protocols are used to detect metastases in sentinel lymph nodes (SLNs), but comparison of the efficacy of these methods is impractical because tissue is lost in processing, making reassessment with another policy difficult. Consequently, performance indicators of this test are largely unknown.DesignThe authors retrospectively examined 112 SLNs removed from 89 patients with breast carcinoma treated at the authors' institution and used the histologic data to devise a mathematic model of a SLN with Matlab modeling software. The authors simulated examination of this computer-generated (virtual) lymph node according to several macroscopic and histologic sampling protocols and for each protocol assessed the probability of detecting micrometastases of specified sizes. The authors used published costing figures to estimate the cost of the policies.ResultsDirect comparison of 6 sectioning strategies currently in use by pathology laboratories showed the chances of detecting a 500-microm metastasis ranged from 20% to 75%. Four of the 6 protocols had a less than 30% chance of detecting metastases of this size. The detection rate of smaller metastases was poorer. Cost was not a good discriminator because some policies were more efficient than others.ConclusionsThe detection of metastases is highly dependent on the methods used to look for them. The authors' simulations suggest that commonly used methods of examining lymph nodes have high false-negative rates, particularly for small metastases. There is an urgent need for pathologists and clinicians to agree on the minimum size of SLN metastases that will be sought by histology and set standard methods for examining these lymph nodes.Gelareh Farshid, Malcolm Pradhan, James Kollias and P. Grantley Gil