1. Fig 2. IHC staining with MMR Proteins
Molecular characterization of colorectal cancer in West Africans
Aliyu Lawan 2,4, Galina F. Khramtsova1, David Irabor3, Mustapha A. Ajani2, Lise Sveen1, Abiola Ibraheem1, Yusuf M. Abdullah4, Henry O. Ebili5, Saad A. Ahmed6, John O. Ogunbiyi2, Olufunmilayo I. Olopade1, Abideen. O Oluwasola2
1. Department of Medicine, Section of Hematology/Oncology, The University of Chicago; 2. Department of Pathology, The University of Ibadan and University College Hospital, Ibadan; Department of Surgery, The University of Ibadan and University College Hospital, Ibadan; 4. Department of Histopathology, Federal Teaching Hospital, Gombe; 5. Department of Pathology, Olabisi Onabanjo University, Sagamu; 6. Department of Pathology, Ahmandu Bello University, Zaria. .
RESULTS
Of the total evaluable CRC cases, 152 of 293 (52%) were males aged between 16 and 90 years, mean age of /-17.57, while there were 141 female cases, with a mean age of / More than a quarter of the cases were under 40 years of age. By our IHC screening algorithm, 140 ( 48%) of the patients had intact MMR proteins, while 153 (52%) patients had at least one MMR protein absent. The most common proteins lost were MLH1/ PMS2 (141 cases, 48.13% of total cases), followed by the loss of MSH2/MSH6 (12 cases, 4.10% of total). Testing of the group in which MLH1/ PMS2 proteins were absent (141 patients) showed mutated BRAF in only 31 cases (22% of this group ). The cases which lack MLH1/ PMS2 and are negative for the BRAF mutation (110 cases), as well as those which are MSH2/MSH6 negative (12 cases) form a group of 122 cases (41.64% of total) which would need additional tests for hypermethylation and referral for genetic counseling.
ABSTRACT
Background: To reduce global disparities in cancer outcomes, there is a need for more concerted efforts to develop the capacity of health care providers to appropriately diagnose and treat common cancers. Colorectal cancer (CRC) incidence in indigenous Africans is significantly lower than in Caucasians but there is a paucity of data on the genetic determinants and molecular biology of colorectal cancer in Nigerians. Lynch syndrome (LS), defined by germline mutation in one of the DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2), is the most common heritable syndrome predisposing to CRC. Loss of MMR proteins can be readily detected by immunohistochemistry (IHC) in both Lynch syndrome and sporadic CRC, and further testing for mutated BRAF protein is helpful in distinguishing Lynch syndrome from sporadic CRC.
Tissue microarray block Slide Tissue core Details of tissue core
Fig 1. Tissue microarray construction
CONCLUSIONS
In this dataset of relatively young onset CRC cases, a large percentage of cases are of the HNPCC subtype. Use of IHC as a universal screening test for all CRC cases, as well as follow-up referral for genetic counseling, could be an innovative approach to CRC cancer control in the population.
MATERIALS AND METHODS
With IRB approval and under a collaborative arrangement with the University of Chicago, seven tissue microarray (TMA) blocks were constructed from CRC samples obtained from the University College Hospital in Ibadan, Federal Teaching Hospital in Gombe, Olabisi Onabanjo University in Sagamu and Ahmadu Bello University in Zaria. TMAs included duplicate 1.0-mm cores of CRC tissue and adjacent normal. For the four MMR proteins, IHC was performed on these TMAs with the following antibodies: MLH1 (Thermo Scientific Pierce Biotech), MSH2 (Life Technologies), MSH6 (Novex), PMS2 (Pierce), anti-BRAF V600E (Roche). All IHC-stained slides (MLH1, MSH2, MSH6, PMS2) were evaluated for expression levels of those proteins in the tumor tissue relative to normal tissue (control) using the following scoring criteria: normal expression was defined as nuclear staining within tumor cells, negative protein expression was defined as complete absence of nuclear staining within tumor cells, and cases with immunoreactivity in 0-10% of tumor cells were scored as equivocal. The slides stained with anti-BRAF V600E (VE1) were scored on a scale of 0 to 3. Strong cytoplasmic staining was scored as 3, medium as 2, 1 as weak, and 0 when the staining was absent.
MLH1 negative
MSH2 negative
ACKNOWLEDGMENTS
Supported by: NIH/Fogerty 5D43 TW International Partnership for Interdisciplinary Research Training; American Cancer Society CRP Genomic Approaches for Primary Prevention of Breast Cancer
Toshio Yoshimatsu, Department of Medicine, Section of Hematology/Oncology, The University of Chicago, Chicago, US; Dr. Patrick A. Akintola, Morbid Anatomy & Histopathology Department, Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State, Nigeria; Dr. Oluwarotimi Bamiro, Morbid Anatomy & Histopathology Department, Olabisi Onabanjo University Teaching Hospital, Sagamu, Ogun State, Nigeria.
MSH2 positive
MLH1 positive
Fig 2. IHC staining with MMR Proteins
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Fig 3. Age and sex distribution of colorectal carcinoma in NG