Rarity of microsatellite genomic instability in B-cell non-Hodgkin's lymphomas in hepatitis C virus-infected patients

Mismatch repair deficiency in hematological malignancies with microsatellite instability

Mutations in human mismatch repair (MMR) genes are the genetic basis for certain types of solid tumors displaying microsatellite instability (MSI). MSI has also been observed in hematological malignancies, but whether these hematological malignancies are associated with MMR deficiency is still unclear. Using both biochemical and genetic approaches, this study analysed MMR proficiency in 11 cell lines derived from patients with hematological malignancies and demonstrated that six out of seven hematological cancer cell lines with MSI were defective in strand-specific MMR. In vitro complementation experiments, using characterized MMR mutant extracts or purified proteins, showed that these hematological cancer cells were defective in either hMutS(alpha) (a heterodimer of hMSH2 and hMSH6) or hMutL(alpha) (a heterodimer of hMLH1 and hPMS2). Furthermore, cell lines deficient in hMutS(alpha) showed large deletions or point mutations in hMSH2, while those deficient in hMutL(alpha) exhibited point mutations in hMLH1 or a lack of expression of hPMS2. From these results, we conclude that, as in solid tumors, hematological malignancies with MSI are also associated with MMR deficiency, and that the cause of MMR deficiency in these cell lines is due to a defective MutS(alpha) or MutL(alpha). We also report here, for the first time, that an MSI-positive cell line derived from Burkitt's lymphoma is proficient in MMR.

Oligoclonal non-neoplastic B cell expansion is the key feature of type II mixed cryoglobulinemia: clinical and molecular findings do not support a bone marrow pathologic diagnosis of indolent B cell lymphoma

OBJECTIVE

Type II mixed cryoglobulinemia (type II MC) is often characterized by features of indolent B cell lymphoma (IBCL) found on pathologic examination of bone marrow, whereas the clinical evidence does not indicate a neoplastic disorder. To better address the issue of indolent malignant versus nonmalignant bone marrow lymphoproliferation underlying type II MC, molecular analyses of B cell clonality were performed in the present study, in conjunction with clinical and pathologic characterization.

METHODS

Polymerase chain reaction DNA amplification of immunoglobulin heavy chain genes was performed in bone marrow biopsy specimens obtained from 15 selected patients with type II MC, all infected with hepatitis C virus. Five of them had also developed overt B cell lymphoma (OBCL) during followup. Bone marrow features were consistent with IBCL in 9 of the 15 patients (group 1) and with reactive lymphoplasmacytosis in 6 of the 15 (group 2).

RESULTS

An oligoclonal B cell expansion was detected in 6 of 9 baseline bone marrow lesions from group 1 patients (biclonal or monoclonal expansion in the remaining 3 cases), and in 6 of 6 from group 2 patients. OBCL was always monoclonal. Selected lesions were analyzed by clonospecific hybridization and by cloning and sequence analysis in patients who had developed OBCL at followup. In 4 of 5 cases, OBCL did not originate from the dominant B cell clones that were overexpanded in the putative neoplastic baseline bone marrow lesions. OBCL clones showed significant homology with rheumatoid factor database sequences.

CONCLUSION

Based on the present results, as well as on evidence from previous studies of liver lesions, oligoclonal non-neoplastic B cell proliferation in the course of chronic infection-related inflammation appears to be the key feature of type II MC. Of note, molecular evidence from target tissues supports the clinical findings both at the time of type II MC diagnosis and in cases of OBCL complication. Bone marrow pathologic findings resembling those of IBCL should thus be considered in the light of clinical and molecular evidence.

Rheumatic syndromes: clues to occult neoplasia

OBJECTIVES

Rheumatic disorders associated with cancer include a variety of conditions, most of which have no features distinguishing them from idiopathic rheumatic disorders. It is generally held that an extensive search for occult malignancy in most rheumatic syndromes is not recommended unless accompanied by specific findings suggestive of malignancy. The objective of this review are to identify rheumatic syndromes associated with cancer, to call attention to features that may suggest the presence of a hidden cancer, and to examine the role to additional clinical and laboratory data as clues to the possible neoplastic cause of those syndromes.

METHODS

A MEDLINE search of the literature dealing with cancer-associated rheumatic syndromes was conducted.

RESULTS

Review of the literature identified significant progress in this area. First, the association of malignancy with certain rheumatic syndromes was convincingly established, such as asymmetric polyarthritis presenting in the elderly with an explosive onset, rheumatoid arthritis with monoclonal gammopathy, Sjögren's syndrome with monoclonality, hypertrophic osteoarthropathy, dermatomyositis, polymyalgia rheumatica with atypical features, Lambert-Eaton myasthenic syndrome, palmar fasciitis and arthritis, eosinophilic fasciitis poorly responsive to corticosteroid therapy, erythema nodosum lasting more than 6 months, and onset of Raynaud's phenomenon or cutaneous leukocytoclastic vasculitis after age 50 years. Second, the list of cancer-associated rheumatic syndromes was extended by including additional entities such as benign edematous polysynovitis, sacroiliitis, adult-onset Still's disease, dermatomyositis sine myositis, systemic sclerosis, Sweet's syndrome, osteomalacia, skeletal hyperostosis, antiphospholipid syndrome, and essential mixed cryoglobulinemia. Third, evidence was provided substantiating that certain long-standing rheumatic syndromes, in particular rheumatoid arthritis, Felty's syndrome, Sjögren's syndrome, dermatomyositis, systemic sclerosis, systemic lupus erythematosus, and temporal arteritis behave like "premalignant conditions." Fourth, it was shown that the recognized tumor markers alpha-fetoprotein, prostate-specific antigen, CA-125, CA 19-9, and CA-3 have low sensitivity and specificity in screening for occult cancer in a population of rheumatic patients, whereas the presence of a monoclonal gammopathy in rheumatoid arthritis and the monoclonal antibody 17-109 in Sjögren's syndrome are reliable signs of malignant transformation.

CONCLUSIONS

The presence of specific rheumatic syndromes and certain clinical and laboratory findings may justify a workup for hidden cancer. Studies of the epidemiology of the cancer-associated rheumatic syndromes and evaluation of the validity of aforementioned clues in prospective studies are goals for future investigations.

Analysis of the frequency of microsatellite instability and p53 gene mutation in splenic marginal zone and MALT lymphomas

AIMS

Studies of the genetic characteristics of splenic marginal zone lymphoma (SMZL) have failed to identify genetic changes specific to this tumour. Microsatellite instability is a type of genomic instability associated with different types of human cancer. Although microsatellite instability is rare in B cell non-Hodgkin's lymphomas, it has been found in some specific subsets, such as marginal zone lymphomas arising in mucosa associated lymphoid tissue (MALT), where an association with p53 mutation has been described. Because it has been proposed that SMZL and MALT are close in histogenetic terms, this study investigated the comparative frequency of microsatellite instability and p53 mutation in patients with SMZL and MALT lymphomas.

METHODS

Microsatellite instability was investigated using seven microsatellite marker loci in 14 patients with SMZL and 20 patients with MALT lymphomas. In an attempt to clarify the role of p53 gene mutation in the pathogenesis of SMZL, exons 5-8 were also investigated by polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) and direct sequencing in a total of 20 patients with SMZL and 22 patients with MALT lymphomas.

RESULTS

Microsatellite instability was not detected in patients with SMZL, although five of 20 patients with MALT lymphomas had microsatellite instability. The frequency of p53 mutation was low in both series (two of 20 patients with SMZL and one of 22 patients with MALT lymphomas). No significant association was found between p53 mutation and microsatellite instability.

CONCLUSIONS

These results indicate that microsatellite instability is not associated with the molecular pathogenesis of SMZL, confirming the relatively increased frequency of microsatellite instability in MALT lymphomas, and perhaps suggesting that MALT and SMZL have different mechanisms of tumorigenesis.