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Letters Intraoperative assessment of axillary lymph nodes in breast cancer

Authors’ reply to Rayter

BMJ 2015; 350 doi: (Published 11 February 2015) Cite this as: BMJ 2015;350:h714
  1. J Michael Dixon, professor of surgery1,
  2. Emiel Rutgers, professor of surgical oncology2,
  3. Kelly K Hunt, professor of surgical oncology 3
  1. 1Edinburgh Breast Unit, Western General Hospital, Edinburgh, UK
  2. 2Netherlands Cancer Institute, Amsterdam, Netherlands
  3. 3University of Texas MD Anderson Cancer Center, Houston, TX, USA
  1. mike.dixon{at}

Rayter raises concerns about our editorial on intraoperative assessment of axillary nodes.1 2 He believes that the meta-analysis of one step nucleic acid amplification (OSNA) is seriously flawed, that it contains a mathematical error, and that the positive predictive value (PPV) should be 0.86 not 0.79.3 The PPV of 0.79 is statistically correct. When calculating the PPV of a relatively rare event its prevalence must be taken into account.4 He has not done this. The PPV of OSNA was even lower in a paper by Rayter’s group. Of …

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