Prognostic scores for patients with salivary adenoid cystic carcinoma without lymph node metastasis.

Adenoid cystic carcinoma (AdCC) of salivary gland grows relatively slowly, but occasionally develops distant metastasis. Although cervical lymph node metastasis (LNM) has been reported as a strong prognostic factor, most of AdCC do not have LNM. In this study, we investigated the prognostic factors to predict disease free survival (DFS), distant metastasis free survival (DMFS), and overall survival (OS) for 175 patients surgically treated for AdCC without LNM, and developed prognostic score (PS) determined as number of positive prognostic factors. The following emerged as significant prognostic factors: positive surgical margin in DFS, pT3/4 and positive surgical margin in DMFS, and positive surgical margin and high-histological grade in OS. 10-year DFS rates were 56.4% in PS0, and 19.1% in PS1 (p < 0.0001). 10-year DMFS rates were 86.3% in PS0, 56.4% in PS1, and 30.7% in PS2 (p < 0.0001). 10-year OS rates were 100% in PS0, 73.3% in PS1, and 38.8% in PS2 (p < 0.0001).

The Landscape of MYB/MYBL1- and Peri-MYB/MYBL1-Associated Rearrangements in Adenoid Cystic Carcinoma.

Approximately 60% of adenoid cystic carcinoma (AdCC) cases are positive for MYB::NFIB or MYBL1::NFIB, whereas MYB/MYBL1 oncoprotein, a key driver of AdCC, is overexpressed in most cases. Juxtaposition of superenhancer regions in NFIB and other genes into the MYB/MYBL1 locus is an attractive oncogenic hypothesis for AdCC cases, either negative or positive for MYB/MYBL1::NFIB. However, evidence supporting this hypothesis is insufficient. We examined 160 salivary AdCC cases for rearrangements in MYB/MYBL1 loci and peri-MYB/MYBL1 areas (centromeric and telomeric areas of 10 Mb each) using formalin-fixed, paraffin-embedded tumor sections. For the detection of the rearrangements, we employed conventional fluorescence in situ hybridization split and fusion assays and a 5 Mb fluorescence in situ hybridization split assay. The latter is a novel assay that enabled us to detect any possible splits within a 5 Mb distance of a chromosome. We found MYB/MYBL1- and peri-MYB/MYBL1-associated rearrangements in 149/160 patients (93%). AdCC cases positive for rearrangements in MYB, MYBL1, the peri-MYB area, and the peri-MYBL1 area numbered 105 (66%), 20 (13%), 19 (12%), and 5 (3%), respectively. In 24 peri-MYB/MYBL1 rearrangement-positive cases, 14 (58%) were found to have a juxtaposition of the NFIB or RAD51B locus into the MYB/MYBL1 loci. On comparing with a tumor group positive for MYB::NFIB, a hallmark of AdCC, other genetically classified tumor groups had similar features of overexpression of the MYB transcript and MYB oncoprotein as detected by semiquantitative RT-qPCR and immunohistochemistry, respectively. In addition, clinicopathological and prognostic features were similar among these groups. Our study suggests that peri-MYB/MYBL1 rearrangements may be a frequent event in AdCC and may result in biological and clinicopathological consequences comparable to MYB/MYBL1 rearrangements. The landscape of MYB/MYBL1 and peri-MYB/MYBL1 rearrangements shown here strongly suggests that juxtaposition of superenhancers into MYB/MYBL1 or peri-MYB/MYBL1 loci is an alteration that acts as a key driver for AdCC oncogenesis and may unify MYB/MYBL1 rearrangement-positive and negative cases.

Pathological evaluation of tumor grade for salivary adenoid cystic carcinoma: A proposal of an objective grading system.

Three pathological grading systems advocated by Perzin/Szanto, Spiro, and van Weert are currently used for adenoid cystic carcinoma (AdCC). In these systems, the amount or presence of the solid tumor component in AdCC specimens is an important index. However, the "solid tumor component" has not been well defined. Salivary AdCC cases (N = 195) were collected after a central pathology review. We introduced a novel criterion for solid tumor component, minAmax (minor axis maximum). The largest solid tumor nest in each AdCC case was histologically screened, the maximum oval fitting the solid nest was estimated, and the length of the minor axis of the oval (minAmax) was measured. The prognostic cutoff for the minAmax was determined using training and validation cohorts. All cases were evaluated for the four grading systems, and their prognostic impact and interobserver variability were examined. The cutoff value for the minAmax was set at 0.20 mm. Multivariate prognostic analyses showed the minAmax and van Weert systems to be independent prognostic tools for overall, disease-free, and distant metastasis-free survival while the Perzin/Szanto and Spiro systems were selected for overall survival but not for disease-free or distant metastasis-free survival. The highest hazard ratio for overall survival (11.9) was obtained with the minAmax system. The reproducibility of the minAmax system (kappa coefficient of 0.81) was scored as very good while those of the other three systems were scored as moderate. In conclusion, the minAmax is a simple, objective, and highly reproducible grading system useful for prognostic stratification for salivary AdCC.

The impact of clinicopathological factors on clinical outcomes in patients with salivary gland adenoid cystic carcinoma: a multi-institutional analysis in Japan.

BACKGROUND: Owing to the low incidence of adenoid cystic carcinoma (AdCC), reliable survival estimates and prognostic factors remained unclarified. METHODS: In this multi-institutional retrospective analysis, we collected 192 AdCC cases, and investigated the impact of clinicopathological factors on clinical outcomes of the patients. All AdCC cases were of salivary gland origin and were surgically treated with curative intent. Diagnoses of AdCC were validated by a central pathology review by expert pathologists. RESULTS: The 5-year overall survival (OS) and disease-free survival (DFS) rates were 92.5 and 50.0%, respectively. Treatment failure occurred in 89 patients (46%) with the distant failures in 65 (34%). Multivariate analysis indicated that pN2 and a pathologically positive surgical margin were independent prognostic factors for both OS and DFS. Histological grade III was an independent prognostic factor for OS. A primary site in the submandibular gland, pT3/4, pN1, and histological grade II were independent prognostic factors for DFS. Postoperative radiation therapy (PORT) improved the locoregional control (LRC) rate. Prophylactic neck dissection was not associated with a better OS or better LRC among patients with cN0. Facial nerve dissection did not improve clinical outcomes in parotid AdCC cases without facial nerve palsy. CONCLUSIONS: A higher TN classification, a pathologically positive surgical margin, and a higher histological grade were associated with a lower OS. PORT improved LRC rates but neck dissection failed to improve clinical outcomes in patients with cN0. As the distant metastasis was frequent, effective systemic therapy is imperative to improve the survival of AdCC patients.

Central pathology review of salivary gland adenoid cystic carcinoma.

BACKGROUND: To assess the role of a central pathology review in the diagnosis of salivary gland adenoid cystic carcinoma (AdCC). METHODS: Surgically resected salivary gland tumors diagnosed as AdCC (n = 219) in 15 reference hospitals in Japan were subjected to a retrospective pathological re-evaluation. RESULTS: After the review, the AdCC diagnosis was revised in 21/219 cases (9.6%). The six benign tumors (2.7%) comprised five basal cell adenomas and one pleomorphic adenoma, and among these six patients, three received postoperative radiotherapy. The remaining 15 malignant tumors (6.8%) comprised nine basal cell adenocarcinomas and six other carcinomas. All revised basal cell adenoma/adenocarcinoma cases were of rare cribriform variants. CONCLUSIONS: A significant proportion of AdCC pathology reports were revised after the central pathology review. It should be emphasized that the greatest attention should be paid in differentiating AdCC from cribriform variant basal cell adenoma/adenocarcinoma, which is very rare in salivary gland tumors.

Ileum preserving expanded jejunectomy and pancreaticoduodenectomy with combined resection of the superior mesenteric artery for huge retroperitoneal solitary fibrous tumor.

We encountered a patient with a large retroperitoneal solitary fibrous tumor, in whom we could preserve approximately 150 cm of the ileum even after pancreaticoduodenectomy combined with resection of the superior mesenteric artery, thus preventing short bowel syndrome.

Postoperative Neutrophil-to-Lymphocyte Ratio as a Predictor of Long-Term Prognosis after Pancreatectomy for Pancreatic Carcinoma: A Retrospective Analysis.

To clarify the prognostic value of the postoperative blood neutrophil-to-lymphocyte ratio (NLR) in patients undergoing pancreatectomy for pancreatic carcinoma (PAC). A high preoperative NLR has been reported to be a predictor of poor survival in patients with various cancers including PAC. However, it has not been extensively examined in postoperative NLR after pancreatectomy for PAC. This retrospective study enrolled 86 patients who underwent pancreatectomy without preoperative therapy for PAC from 2005 to 2013. Clinicopathological parameters, including postoperative NLR, were evaluated to identify predictors of the overall and recurrence-free survival of patients after pancreatectomy. Univariate and multivariate analyses were performed, using the Cox proportional hazards model. Univariate and multivariate analyses showed that postoperative NLR at one month was an independent prognostic factor in the overall and recurrence-free survival of patients. The 3-year survival rate after pancreatectomy was as follows: 33.9 per cent in patients with a postoperative NLR of less than 3.0 at one month; and 7.3 per cent in those with a postoperative NLR of 3.0 or more at one month (P < 0.001). The overall survival rate after pancreatectomy in the NLR at one month ≥3.0 group was significantly lower than in the NLR at one month <3.0 group: one year, 42.6 versus 81.9 per cent; three year, 7.3 versus 33.9 per cent (P < 0.001). The results of the study suggest that the postoperative NLR at one month is an independent predictor of survival after pancreatectomy in patients with PAC.

Low-grade intraductal carcinoma (low-grade cribriform cystadenocarcinoma) with tumor-associated lymphoid proliferation of parotid gland.

We report a rare case of low-grade intraductal carcinoma with tumor-associated lymphoid proliferation (TALP) in the parotid gland of a 75-year-old woman. Grossly, the tumor was solid and cystic. Histologically, the tumor consisted of a papillary-cystic, micropapillary, or focally cribriform proliferations of epithelial cells with low-grade cytological atypia. The interspaces between the epithelial components were filled with prominent lymphoid stroma and lymphoid follicles, superficially mimicking Warthin tumor. The neoplastic epithelial cells were positive for S100 protein by immunohistochemical staining. There was an attenuated layer of myoepithelial cells all around the epithelial components, indicating a non-invasive (in situ) nature. Although TALP is a rare finding in intraductal carcinoma, it should be considered as a histological variation of this kind of tumor. The relationship between intraductal carcinoma, low-grade cribriform cystadenocarcinoma, low-grade salivary duct carcinoma, and salivary duct carcinoma in situ is also discussed in this report.

Neuroendocrine carcinoma of the esophagus: Clinicopathological and immunohistochemical features of 14 cases.

BACKGROUND: Neuroendocrine carcinoma (NEC) of the esophagus is a rare and highly aggressive disease but the biological features are poorly understood. The objective of this study was to analyze the clinicopathological and immunohistochemical features of NEC of the esophagus. METHODS: Fourteen patients diagnosed with NEC of the esophagus from 1998 to 2013 were included in this study. Clinicopathologic features, therapeutic outcomes and immunohistochemical results were analyzed. RESULTS: Eleven out of 14 cases showed protruding or localized type with or without ulceration. Only three patients were negative for both lymph node and organ metastasis and seven cases were positive for metastases to distant organs and/or distant lymph nodes. Of the six patients with limited disease (LD), three patients were treated by surgery. Three patients with LD and seven patients with extensive disease (ED) were initially treated with chemotherapy, except for one who underwent concurrent chemo-radiotherapy due to passage disturbance. The median survival of patients with LD was 8.5 months, whereas that of patients with LD was 17 months. Among the 14 cases, 12 cases (83.3%), 13 cases (91.7%) and 12 cases (83.3%) showed positive immunostaining for choromogranin A, synaptophysin and CD56, respectively. Nine of 14 cases (64.2%) presented positive staining for c-kit and most (8/9, 88%) simultaneously showed p53 protein abnormality. Two cases were negative for c-kit and p53, and positive for CK20. CONCLUSION: Consistent with previous reports, the prognosis of NEC of esophagus is dismal. From the results of immunohistochemical study, NEC of esophagus might be divided into two categories due to the staining positivity of c-kit and p53. This study provides new insight into the biology of NEC of the esophagus.

Mutations of the EGFR, K-ras, EML4-ALK, and BRAF genes in resected pathological stage I lung adenocarcinoma.

BACKGROUND AND PURPOSE: The EGFR, K-ras, EML4-ALK, and BRAF genes are oncogenic drivers of lung adenocarcinoma. We conducted this study to analyze the mutations of these genes in stage I adenocarcinoma. METHODS: The subjects of this retrospective study were 256 patients with resected stage I lung adenocarcinoma. We analyzed mutations of the EGFR, K-ras, and BRAF genes, and the EML4-ALK fusion gene. We also assessed disease-free survival (DFS) to evaluate the prognostic value and overall survival (OS) to evaluate the predictive value of treatment after recurrence. RESULTS: Mutations of the EGFR, K-ras, EML4-ALK, and BRAF genes were detected in 120 (46.8 %), 14 (5.5 %), 6 (2.3 %), and 2 (0.8 %) of the 256 tumors. Two tumors had double mutations (0.8 %). The incidence of EGFR mutations was significantly higher in women than in men. The EML4-ALK fusion gene was detected only in younger patients. The DFS and OS of the K-ras mutant group were significantly worse than those of the EGFR mutant group, the EML4-ALK fusion gene group, and the wild-type group. Six of the seven patients with the EML4-ALK fusion gene are still alive without recurrent disease. CONCLUSIONS: In patients with stage I adenocarcinoma, mutation of the K-ras gene was a poor prognostic factor for recurrence. The presence of a mutation of the EGFR or EML4-ALK gene was not a prognostic factor.

Suture granuloma with false-positive finding on PET/CT after gastrectomy for gastric cancer.

This study is a case report on a 49-year-old woman who had a gastrectomy and lymphadenectomy for pStage IIIa gastric cancer. Shortly after a 12-month course of adjuvant chemotherapy, CT showed a nodule adjacent to the gallbladder. High (18) F-fluorodeoxyglucose accumulation was detected, with a standardized uptake value of 10. Therefore, laparoscopic excision was performed for diagnosis and treatment. The histopathological finding was suture granuloma. Suture granulomas with high standardized uptake values on PET scans are uncommon and often cause surgeons to provide an inaccurate diagnosis. Our study suggests that suture granuloma should be included in the differential diagnosis of a new or recurrent mass detected in patients with a history of prior surgery; however, surgeons must bear in mind that false-positive fluorodeoxyglucose-PET results can be observed in suture granuloma.

Dual gain of HER2 and EGFR gene copy numbers impacts the prognosis of carcinoma ex pleomorphic adenoma.

We investigated the potential roles of HER2 and EGFR and evaluated their prognostic significance in carcinoma ex pleomorphic adenoma (CXPA). We analyzed HER2 and EGFR overexpression status using immunohistochemistry (IHC) and gene copy number gain by chromogenic in situ hybridization (CISH) in 50 cases of CXPA (40 ductal-type and 10 myoepithelial-type CXPAs). Salivary duct carcinoma was the most common histologic subtype of malignant component (n = 21). Immunohistochemistry positivity and chromogenic in situ hybridization positivity were closely correlated in both HER2 and EGFR. HER2 CISH positivity (mostly gene amplification) and EGFR CISH positivity (mostly gene high polysomy) were present in 19 (40%) and 21 (44%) cases, respectively, and were each significantly correlated with poor outcome (P = .0009 and P = .0032, respectively). Dual gain of HER2 and EGFR gene copy numbers was present in 11 cases (23%) and was the most aggressive genotype. HER2 CISH positivity was more frequently present in ductal-type CXPAs (47%) than in myoepithelial-type CXPAs (10%), whereas the prevalence of EGFR CISH positivity was similar in both histologic subtypes (42% and 50%, respectively). Our results suggest that HER2 and EGFR gene copy number gains may play an important role in the progression of CXPA, in particular ductal-type CXPAs. HER2 CISH-positive/EGFR CISH-positive tumors may be the most aggressive subgroup in CXPA. The molecular subclassification of CXPA based on the HER2 and EGFR status may be helpful for prognostic prediction and decisions regarding the choice of therapeutic strategy.

Successful treatment of primary jejunal cancer after esophageal and colon cancer resection.

Patients with esophageal cancer are susceptible to other primary cancers, but multiple primary cancers involving the esophagus and jejunum are rare. We herein report a case of primary jejunal cancer as a component of metachronous triple primary cancers including esophageal cancer and ascending colon cancer. A 63-year-old male patient with a history of surgery for esophageal cancer and ascending colon cancer was admitted to our hospital after experiencing 1 month of repeated vomiting and epigastric abdominal pain. Esophagogastroduodenoscopy, duodenography, and computed tomography revealed a jejunal tumor located 2 cm from the ligament of Treitz on the anal side. Partial resection of the jejunum with lymph node dissection was performed. The postoperative course was uneventful, and the patient remains well with no signs of recurrence 10 months after the operation. This is the first report of curative resection of triple primary cancers of the esophagus, jejunum, and colon. Patients with a history of esophageal cancer are susceptible to other primary cancers, and it is important to perform surveillance for the subsequent development of other cancers.

Mismatch repair deficient mice show susceptibility to oxidative stress-induced intestinal carcinogenesis.

We have previously established an experimental system for oxidative DNA damage-induced tumorigenesis in the small intestine of mice. To elucidate the roles of mismatch repair genes in the tumor suppression, we performed oxidative DNA damage-induced tumorigenesis experiments using Msh2-deficient mice. Oral administration of 0.2% Potassium Bromate, KBrO3, effectively induced epithelial tumors in the small intestines of Msh2-deficient mice. We observed a 22.5-fold increase in tumor formation in the small intestines of Msh2-deficient mice compared with the wild type mice. These results indicate that mismatch repair is involved in the suppression of oxidative stress-induced intestinal tumorigenesis in mice. A mutation analysis of the Ctnnb1 gene of the tumors revealed predominant occurrences of G:C to A:T transitions. The TUNEL analysis showed a decreased number of TUNEL-positive cells in the crypts of small intestines from the Msh2-deficient mice compared with the wild type mice after treatment of KBrO3. These results suggest that the mismatch repair system may simultaneously function in both avoiding mutagenesis and inducing cell death to suppress the tumorigenesis induced by oxidative stress in the small intestine of mice.

Protein-bound polysaccharide-K reduces colitic tumors and improves survival of inflammatory bowel disease in vivo.

Protein-bound polysaccharide-K (PSK) is a biological response modifier that possesses antitumor effects against various tumors. Although an inflammatory response has been considered to play an important role in the development of colorectal cancer, the anti-inflammatory effect of PSK has yet to be elucidated. An inflammatory bowel disease (IBD)-induced colorectal tumor model with 1.2-dimethyl hydrazine (DMH) and dextran sodium sulfate (DSS) was used to examine the effects of PSK on tumor suppression and survival. Although 90% of the mice that were not treated with PSK developed colitic tumors, oral administration of PSK suppressed tumor formation by less than 30%. Although deaths associated with DSS-induced melena were observed, PSK significantly reduced mortality. In conclusion, the present study showed that PSK not only suppressed colorectal tumor formation in the DMH+DSS-induced IBD model, but also improved the survival rate, indicating that anti-inflammatory activity is one of the mechanisms for the antitumor effects of PSK.

Y-box binding protein-1 (YB-1) promotes cell cycle progression through CDC6-dependent pathway in human cancer cells.

Y-box binding protein-1 (YB-1) plays pivotal roles in acquisition of global drug resistance and cell growth promotion through transcriptional activation of genes for both drug resistance and growth factor receptors. In this study, we investigated whether YB-1 is involved in regulation of the cell cycle and cell proliferation of human cancer cells. Treatment with YB-1 siRNA caused a marked suppression of cell proliferation and expression of a cell cycle related gene, CDC6 by cancer cells. Of cell cycle of cancer cells, S phase content was specifically reduced by knockdown of YB-1. The overexpression of CDC6 abrogated this inhibition of both cell proliferation and S phase entry. ChIP assay demonstrated that YB-1 binds to a Y-box located in the promoter region of the CDC6 gene. Expression of cyclin D1, CDK1 and CDK2 was also reduced with increased expression of p21(Cip1) and p16(INK4A) when treated with YB-1 siRNA. Furthermore, the nuclear YB-1 expression was significantly associated with the level of CDC6 nuclear expression in patients with breast cancer. In conclusion, YB-1 plays an important role in cell cycle progression at G1/S of human cancer cells. YB-1 thus could be a potent biomarker for tumour growth and cell cycle in its close association with CDC6.

A comprehensive analysis of immunohistochemical studies in intrahepatic cholangiocarcinoma using the survival tree model.

OBJECTIVE: Various immunohistochemical studies have been performed regarding intrahepatic cholangiocarcinoma (ICC), including the cell cycle-related proteins (p27, cyclin D1, 14-3-3sigma, p53, cyclin B1 and Ki-67), the proto-oncogenes (c-erbB-2 and c-Met), the extracellular matrix proteins (tenascin and laminin) and others (beta-catenin, epidermal growth factor receptor, osteopontin, aquaporin 1, MUC5AC and fascin). Nevertheless, none of these have been proven to be a predictive power of the prognosis with high specificity and sensitivity for ICC. METHODS: Sixty-one patients with ICC were selected and ICC specimens were immunohistochemically stained with the above 16 markers, as previously reported. RESULTS: The immunoreactivity of osteopontin, tenascin and Ki-67 divided the patients with ICC into 4 subgroups by the survival tree model. There was a significant relationship between the location of the tumor, TNM classification, histological differentiation, tumor size, lymphatic permeation, perineural invasion, lymph node metastasis, intrahepatic metastasis and viral infection among the 4 subgroups. In addition, there was a significant difference in survival among the 4 subgroups. CONCLUSION: In this study, the subgrouping by the survival tree model might be helpful for predicting the patients' prognosis in ICC.

Overexpression of class III beta-tubulin predicts good response to taxane-based chemotherapy in ovarian clear cell adenocarcinoma.

PURPOSE: Of the various microtubule-associated molecules, beta-tubulin III has been reported to be closely associated with the therapeutic efficacy of taxane-based chemotherapy against ovarian cancer. Stathmin and microtubule-associated protein 4 (MAP4) have been reported to play an important role in microtubule stabilization. In this study, we investigated whether expression of these microtubule-associated factors affects the therapeutic efficacy of taxane-based chemotherapy in ovarian clear cell adenocarcinoma. EXPERIMENTAL DESIGN: Drug sensitivity of paclitaxel or cisplatin was assessed in ovarian cancer cell lines treated with small interfering RNA of tubulin isoforms, MAP4, and stathmin. We examined 94 surgically resected ovarian clear cell adenocarcinoma specimens from patients treated with taxane-containing regimens (n=44) and with taxane-free regimens (n=50), using immunohistochemistry to detect expression of beta-tubulin III, stathmin, and MAP4. RESULTS: Knockdown of beta-tubulin III and IV specifically conferred drug resistance to paclitaxel in one ovarian cancer cell line, but not to other molecules. Estimated overall survival revealed a significant synergistic effect between taxane and beta-tubulin III in patients with ovarian clear cell adenocarcinoma. Of three microtubule-related molecules, among the taxane-based chemotherapy group, cases with higher beta-tubulin III expression were associated with a significantly more favorable prognosis compared with those having lower beta-tubulin III expression. By contrast, there was no statistical significance in the synergistic relationships between stathmin and taxane or between MAP4 and taxane. CONCLUSIONS: Taxane-based chemotherapy was effective for patients with ovarian clear cell adenocarcinomas who were positive for beta-tubulin III but not for those who were negative for these proteins.

Simulation-based analyses reveal stable microsatellite sequences in human pancreatic cancer.

Genomic analysis using tissue samples is an essential approach in cancer genetics. However, technical and biological limits exist in this approach. Microsatellite instability (MSI) is frequently observed in human tumors. MSI assays are now prevalent and regarded as commonplace. However, several technical problems have been left unsolved in the conventional assay technique. Indeed, the reported frequencies of MSI differ widely in each malignancy. An example is pancreatic cancer. Using a unique fluorescent technique, we found that MSI is extremely infrequent in this malignancy, despite the relatively high frequencies in some reports. In a series of simulations, we have demonstrated that the extremely low frequency was derived neither from less sensitive assays nor from a scarcity of cancer cells in tissue samples. Furthermore, analyzing laser-capture microdissection (LCM)-processed cell populations of a microsatellite-unstable colorectal cancer cell line, HCT116, we have shown that MSI can be detected only when comparing two cell populations that have grown independently to a sufficiently large size. When MSI is not detected in analyses using tissue samples, LCM is not advisable. We therefore did not extend our study to LCM of tissue specimens. We conclude that microsatellite sequence alterations are not detectable in human pancreatic cancer.

Two modes of microsatellite instability in human cancer: differential connection of defective DNA mismatch repair to dinucleotide repeat instability.

Microsatellite instability (MSI) is associated with defective DNA mismatch repair in various human malignancies. Using a unique fluorescent technique, we have observed two distinct modes of dinucleotide microsatellite alterations in human colorectal cancer. Type A alterations are defined as length changes of < or =6 bp. Type B changes are more drastic and involve modifications of > or =8 bp. We show here that defective mismatch repair is necessary and sufficient for Type A changes. These changes were observed in cell lines and in tumours from mismatch repair gene-knockout mice. No Type B instability was seen in these cells or tumours. In a panel of human colorectal tumours, both Type A MSI and Type B instability were observed. Both types of MSI were associated with hMSH2 or hMLH1 mismatch repair gene alterations. Intriguingly, p53 mutations, which are generally regarded as uncommon in human tumours of the MSI+ phenotype, were frequently associated with Type A instability, whereas none was found in tumours with Type B instability, reflecting the prevailing viewpoint. Inspection of published data reveals that the microsatellite instability that has been observed in various malignancies, including those associated with Hereditary Non-Polyposis Colorectal Cancer (HNPCC), is predominantly Type B. Our findings indicate that Type B instability is not a simple reflection of a repair defect. We suggest that there are at least two qualitatively distinct modes of dinucleotide MSI in human colorectal cancer, and that different molecular mechanisms may underlie these modes of MSI. The relationship between MSI and defective mismatch repair may be more complex than hitherto suspected.