1. A Retrospective Analysis of Microsatellite Instability testing on colorectal cancer specimens in Queensland Public Hospitals
Matthew Burge; Hayden Christie; Lakshmy Nandakumar; Melissa Eastgate; David Wyld; Mahendra Singh
Royal Brisbane and Women’s Hospital; Bowen Bridge Road; Herston; 4029; QLD
Background
Results
Results Continued
Microsatellite Instability (MSI) can result from germ line mutation of the genes encoding the mismatch repair proteins (HNPCC) or somatic inactivation, by promoter methylation, most commonly of the MLH1 mismatch repair gene.1 The four MMR genes that contribute to MSI are MSH2, MLH1, MSH6 and PMS2.2
MSI tumours account for 15-20% of all CRC’s with HNPCC contributing 3-5%.3 Studies demonstrate that MSI is reliably detected by immunohistochemistry of the mismatch repair proteins. This simple method also identifies the abnormal protein hence guides subsequent investigations. Given the poor sensitivity of clinical characteristics in identifying HNPCC subjects, there is increasing call to routinely test all incident CRC patients.4
Detecting HNPCC is important for both patients and their family in regards to cancer prevention and surveillance.3 BRAF (V600E) mutations occur in around 50% of MSI due to MLH1 promoter hypermethylation but do not occur in HNPCC. Therefore, when MLH 1 is lost, testing for the BRAF mutation is useful as its presence can reliably exclude HNPCC as the cause.5
Mismatch repair (MMR) is involved in cell death after DNA damage, thus MMR defective cells might be less likely to respond to fluorouracil (FU) based chemotherapy.6,7 Whilst there is some literature supporting this notion, it remains contentious.
There is no doubt that MSI CRC is associated with a better prognosis, especially in stage 2 where the hazard ratio for recurrence is approximately , but also in stage 3.8,9 Given the limited benefit from chemotherapy in unselected stage 2 patients, MSI patients with such a good prognosis should not receive adjuvant therapy.3 Our understanding of the role for chemotherapy in stage 3 MSI is evolving, but currently oxaliplatin/FU is the standard. The frequency of MSI testing, and who is chosen for it, is currently unclear in Queensland.
As a prelude to routine incorporation of MSI testing into the pathology report of colorectal cancer specimens, we retrospectively analysed testing in Queensland public hospitals
There were 181 tumours among 177 patients. 61 (34%) of patients were tested. All 4 proteins were tested in 56 patients. Fifteen patients (24% of those tested or 8% of all patients) demonstrated loss of at least 1 MMR protein.
Among the fifteen tumours with protein loss, 11 had combined loss of MLH1 and PMS2; 1 isolated MSH6; 1 isolated PMS2; 1 combined MSH 2 and MSH 6 loss; and 1 isolated MLH 1. Among the 12 patients with MLH 1 loss, BRAF mutation was tested in 6 (50%). An explanation of the abnormal MMR result was offered in 10 (67%) of patients.
44% of all tumours were right sided, increasing to 63% of those tested. Among patients under 50, 55% were tested versus 32% of those older than 50 (p=0.051).
Conclusion
MSI testing is performed in a minority of patients. There is a trend to more commonly test younger patients and those with right sided tumours. When testing is performed, an explanation of the result is often not provided. When MLH1 is lost, BRAF testing is undertaken in approximately half the cases.
We estimate that currently only 1/3 of public MSI cases are currently being identified. The implementation of universal testing accompanied by an algorithm for dealing with abnormal results is likely to increase HNPCC detection and, in some cases, assist oncologists in therapy selection.
References
Kane MF, Loda M, Gaida GM, et al: Methylation of the hMLH1 promoter correlates with lack of expression of hMLH1 in sporadic colon tumors and mismatch repair-defective human tumor cell lines. Cancer Res 57: , 1997.
Parsons R, Li G-M, Longley MJ, et al. Hypermutability and mismatch repair deficiency in RER+ tumor cells. Cell 75:1227–1236, 1993.
De la Chapelle A, Hampel H: Clinical relevance of microsatellite instability in colorectal cancer. J Clin Oncol 26: , 2010.
Hampel H, et al. Feasibility of Screening for Lynch Syndrome Among Patients With Colorectal Cancer. J Clin Oncol 26: , 2008.
Bessa X, Balleste B, Andreu M, et al. A prospective, multicenter, population-based study of BRAF mutational analysis for Lynch syndrome screening. Clin Gastrenterol Hepatol 6:206–
Branch P, Aquilina G, Bignami M, et al: Defective mismatch binding and a mutator phenotype in cells tolerant to DNA damage. Nature 362: , 1993.
Boland CR: Clinical uses of microsatellite instability testing in colorectal cancer: an ongoing challenge. J Clin Oncol 25: , 2007.
Sargent DJ, et al. Prognostic impact of deficient mismatch repair (dMMR) in 7,803 stage II/III colon cancer (CC) patients (pts): A pooled individual pt data analysis of 17 adjuvant trials in the ACCENT database. J Clin Oncol (Meeting Abstracts) 32:suppl; abstr 3507, 2014.
Hutchins G, et al. Value of Mismatch Repair, KRAS, and BRAF Mutations in Predicting Recurrence and Benefits From Chemotherapy in Colorectal Cancer. J Clin Oncol 29: , 2011.
Methods & Materials
An electronic database of public pathology specimens of resected primary colorectal cancers in Queensland (AUSLAB) was searched from November 2012 to November 2013.
For each report we analysed whether MSI testing by IHC was performed, the results, and whether an explanation of the result was included. We analysed testing as a function of patient demographics.