Annals of Oncology 14:1530-1536, 2003
© 2003 European Society for Medical Oncology
Original Paper |
Microsatellite instability and mutation analysis among southern Italian patients with colorectal carcinoma: detection of different alterations accounting for MLH1 and MSH2 inactivation in familial cases
1 Istituto Chimica Biomolecolare-Sezione di Sassari, C.N.R., Tramariglio, Alghero; 2 Istituto di Anatomia Patologica, Università di Sassari, Sassari; 3 Istituto Nazionale Tumori ‘G. Pascale’, Napoli; 4 Chirurgia Generale II, Università di Cagliari, Cagliari; 5 Chirurgia Generale e Vascolare e Oncologia Clinica, Università di Bari, Bari; 6 Anatomia Patologica, Ospedali Riuniti, Foggia; 7 Medicina Nucleare, Università di Sassari, Viale San Pietro, Sassari, Italy
Received 12 February 2003; revised 7 April 2003; accepted 15 April 2003
Background:
Microsatellite instability (MSI) is due to defective DNA mismatch repair (MMR) and has been detected at various rates in colorectal carcinoma (CRC). The role of MSI in colorectal tumorigenesis was assessed further in this study by both microsatellite analysis of two CRC subsets [unselected patients (n = 215) and patients <50 years of age (n = 95)], and mutation screening of the two major MMR genes MLH1 and MSH2 among familial CRC cases.
Patients and methods:
PCR-based microsatellite analysis was performed on paraffin-embedded tissues. In CRC families, MLH1/MSH2 mutation analysis and MLH1/MSH2 immunostaining were performed on germline DNA and MSI+ tumour tissues, respectively.
Results:
The MSI+ phenotype was detected in 75 (24%) patients, with higher incidence in early-onset or proximally located tumours. Among 220 patients investigated for family cancer history, MSI frequency was markedly higher in familial [18/27 (67%)] than in sporadic [32/193 (17%)] cases. Three MLH1 and six MSH2 germline mutations were identified in 14 out of 36 (39%) CRC families. Prevalence of MLH1/MSH2 mutations in CRC families was significantly increased by the presence of: (i) fulfilled Amsterdam criteria; (ii) four or more CRCs; or (iii) one or more endometrial cancer. While MSH2 was found mostly mutated, almost all [8/9 (89%)] familial MSI+ cases with loss of the MLH1 protein were negative for MLH1 germline mutations.
Conclusions:
Both genetic (for MSH2) and gene-silencing (for MLH1) alterations seem to be involved in CRC pathogenesis.
Key words: colorectal cancer, gene inactivation, microsatellite instability, MLH1/MSH2 germline mutations