Should pathologists send all or only selected slides for patient-requested interlaboratory second opinion?

For interlaboratory second opinions requested by patients or clinicians, whether all or selected slides should be sent is unknown. We compared the disagreement rate for requested second opinions for 4 years of sending selected slides with the rate for 1 year of sending all slides. Disagreements were identified in 81 (13.6%) of 596 cases (468 selected slides, 128 all slides). The disagreement rate was less when sending selected slides (n = 58 [12%]) vs all slides (n = 23 [18%]; P = .03). Only 5 cases were identified with disagreement related to whether all or selected slides were sent (selected slides, 1 case [slide of interest inadvertently not chosen]; all slides, 4 cases; P = .03). When all slides were sent (disagreement in number of positive nodes, 2 cases; failure of second laboratory to identify microinvasive ductal carcinoma when present in 1 of 10 core biopsy slides, and ductal carcinoma in situ [DCIS] adjacent to invasive ductal carcinoma when DCIS present on only 1 of 5 slides [2/81 (2%)], 1 case each). Sending all slides is associated with a higher disagreement rate than sending only selected slides, but this disagreement comes from correcting and introducing error.