Discordance between immunochemistry of mismatch repair proteins and molecular testing of microsatellite instability in colorectal cancer

Background

DNA mismatch repair system deficiency (dMMR) is found in 15% of colorectal cancers (CRCs). Two methods are used to determine dMMR, immunohistochemistry (IHC) of MMR proteins and molecular testing of microsatellite instability (MSI). Only studies with a low number of patients have reported rates of discordance between these two methods, ranging from 1% to 10%.

Materials and methods

Overall, 3228 consecutive patients with CRCs from two centers were included. Molecular testing was carried out using the Pentaplex panel and IHC evaluated four (MLH1, MSH2, MSH6, and PMS2; cohort 1; n = 1085) or two MMR proteins (MLH1 and MSH2; cohort 2; n = 2143). The primary endpoint was the rate of discordance between MSI and MMR IHC tests.

Results

Fifty-one discordant cases (1.6%) were initially observed. Twenty-nine out of 51 discordant cases were related to IHC misclassifications. In cohort 1, after re-reading IHC and/or carrying out new IHC, 16 discordant cases were reclassified as nondiscordant. In cohort 2, after the addition of MSH6/PMS2 IHC and re-examination, 13 were reclassified as nondiscordant. In addition, 10 misclassifications of molecular tests were identified. Finally, only 12 discordant cases (0.4%) remained: 5 were proficient MMR/MSI and 7 were dMMR/microsatellite stable.

Conclusions

Our study confirmed the high degree of concordance between MSI and MMR IHC tests. Discordant cases must be reviewed, and if needed, tests must be repeated and analyzed by an expert team.

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Concordance between MMR IHC (four proteins) and MSI molecular testing (Pentaplex) is superior to 98% in CRC cases

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Most discordant cases are related to misinterpretation of the tests, which may lead to clinical management errors.

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Discordant cases must be reviewed and tests must be repeated because most cases will be reclassified as nondiscordant.

A comparison of ropivacaine and bupivacaine for cervical plexus block

We compared bupivacaine 0.5% and ropivacaine 0.75% for cervical plexus block (CB). Forty patients scheduled for carotid artery surgery were allocated randomly to undergo superficial and deep CB with 30 mL of one of the two anesthetic solutions. We evaluated the onset of anesthetic block; the requirement for supplementation during the surgery; the patients' satisfaction; postoperative pain on a visual analog scale at 1, 2, and 3 h; and the use of paracetamol as a rescue analgesic medication. Arterial blood was sampled immediately and 1, 3, 5, 10, 15, 30, 45, and 60 min after CB for measurements of bupivacaine or ropivacaine concentrations. Patients in both groups had equivalent onset of CB, local infiltration with lidocaine during surgery, and satisfaction scores. In the Bupivacaine group, visual analog scale scores were lower at 2 and 3 h, and the delay before paracetamol administration was prolonged. Observed peak concentrations were larger in the Ropivacaine group (4.25 [2.07-6.59 mg/L] vs 3.02 [0.98-5.82 mg/L]), but time to reach peak concentrations was comparable (5 [1-15 min] vs 5 [0-45 min] in the Ropivacaine and Bupivacaine groups, respectively). We conclude that ropivacaine has no advantage over bupivacaine for CB.

IMPLICATIONS

Compared with bupivacaine (150 mg), a larger dose of ropivacaine (225 mg) produces comparable features of cervical plexus block but less postoperative analgesia and larger plasma concentrations. There is no reason to favor ropivacaine in such a case.

Intrathecal sufentanil and morphine for post-thoracotomy pain relief

In this double-blind randomized study we compared a group of 15 patients undergoing thoracotomy who received a spinal injection of sufentanil 20 microg combined with morphine (200 microg) after induction of general anaesthesia with a control group of the same size. Post-operative pain was rated on a visual analogue scale (VAS) and a verbal rating scale at rest and with a VAS on coughing. In the recovery room, patients received titrated i.v. morphine until the VAS score was <30, and were followed by patient-controlled analgesia (PCA) for 72 h. The intrathecal sufentanil and morphine group had a lower intra-operative requirement for i.v. sufentanil and needed less i.v. morphine for titration in the recovery room. I.v. PCA morphine consumption and pain scores were lower in the active group than in the control group during the first 24 h. There were no differences after this time. Spirometric data (peak expiratory flow, forced vital capacity and forced expiratory volume in 1 s) were similar in the two groups. We conclude that the combination of intrathecal sufentanil and morphine produces analgesia of rapid onset and with a duration of 24 h.