Figure 3

Performance of various microscopic sectioning protocols for detecting occult micrometastases. (a–e) All SLNs were grossly sectioned at close to 2.0 mm thick sections. (a) The reference protocol examined one section from the top of the block. All cases with negative initial sections were evaluated with protocol (e); protocols (b–d) were simulated by examining only specific sections from protocol (e). Detection rates for micrometastases >0.2 mm and no larger than 2.0 mm (Micromet) and ITCs no larger than 0.2 mm (ITC) were calculated for each protocol. (b) Two additional sections separated by 0.18 mm. (c) Two additional sections separated by 0.5 mm. (d) Four additional sections separated by 0.5 mm. (e) Multiple additional sections separated by 0.18 mm completely through the block (median 11 sections per block). Only protocol (e) can reliably detect all micrometastases present but will still miss ITCs. The maximum size of missed metastases is dependent on the thickness of tissue not examined between each section or remaining in the block. Protocols (c) and (d) are compromise protocols that perform better than protocol (b) and do not perform as well as protocol (e) but are less expensive and less time consuming than protocol (e). (Data adapted from Ref. ¹²).