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Correspondence
OSNA testing for lymph node staging in colorectal cancer
  1. Richard Colling1,
  2. Trevor Yeung2,
  3. Roel Hompes2,
  4. Rebecca Kraus2,
  5. Ronan Cahill2,
  6. Neil Mortensen2,
  7. Lai Mun Wang1
  1. 1Department of Cellular Pathology, Oxford University Hospitals NHS Trust, Oxford, UK
  2. 2Nuffield Department of Surgical Sciences, University of Oxford, Oxford, UK
  1. Correspondence to Dr Richard Colling, Cellular Pathology, Level 1, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK; rtcolling{at}gmail.com

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Lymph node staging in colorectal cancer (CRC) is established by histological examination. Molecular techniques, such as one-step nucleic acid amplification (OSNA), have been recommended by NICE1 for intraoperative sentinel node assessment in breast cancer. OSNA is a relatively novel and simple molecular technique that uses a reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP) reaction to detect tumour specific (CK19) mRNA in lymph nodes. We aim to provide unbiased data on the diagnostic accuracy of OSNA in detecting CRC nodal metastases and feedback the practicalities of running such a service in an National Health Service (NHS) cellular pathology department.

Consent was sought from consecutive patients undergoing elective resection for any stage CRC over a 14-month period (November 2013–December 2014). Stented tumours and perforated cases were excluded.

Resected specimens were received fresh, inked according to standard guidelines and lymph nodes were dissected. Each harvested node was bisected—one half was fixed in 10% formalin for routine histology and the other was snap-frozen in liquid nitrogen and stored at −80°C for OSNA processing. The remaining specimen was fixed and subsequently dissected for standard histology. OSNA assaying was performed as per manufacturers' instructions. Lymph nodes weighing >0.05 g were analysed in a single assay and those <0.05 g were combined for processing. Nodes were homogenised in lysis buffer (Lynorhag; Sysmex) and …

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