Vacuum-assisted large-core needle biopsy (VLNB) improves the management of patients with breast microcalcifications - analysis of 1009 cases.

AIMS: To evaluate the surgical management of patients who underwent VLNB for breast microcalcifications. METHODS: This retrospective study compared the histological results and the surgical procedures in two groups of patients, group 1: large-core needle biopsy n=1009, and group 2: surgical biopsy n=270. RESULTS: After VLNB, 54% patients were not operated on after stereotactic large-core needle biopsy, 42% underwent one operation, 4% underwent two operations and 0.2% underwent three operations. No surgery was performed for 95% of benign lesions. Multiples operations were necessary in 12% of patients with malignant lesions of VLNB group compared to 45% in the surgical biopsy group. The rate of underdiagnosis of borderline lesions and ductal carcinomas in situ was 16% by the large-core biopsy technique. CONCLUSION: VLNB constitutes an alternative to surgical biopsy. This procedure avoids surgery for most benign lesions and reduces the number of surgical procedures in malignant lesions.

An atypical topoisomerase II from Archaea with implications for meiotic recombination.

Type II topoisomerases help regulate DNA topology during transcription, replication and recombination by catalysing DNA strand transfer through transient double-stranded breaks. All type II topoisomerases described so far are members of a single protein family. We have cloned and sequenced the genes encoding the A and B subunits of topoisomerase II from the archaeon Sulfolobus shibatae. This enzyme is the first of a new family. It has no similarity with other type II topoisomerases, except for three motifs in the B subunit probably involved in ATP binding and hydrolysis. We also found these motifs in proteins of the Hsp90 and MutL families. The A subunit has similarities with four proteins of unknown function. One of them, the Saccharomyces cerevisiae Spo11 protein, is required for the initiation of meiotic recombination. Mutagenesis, performed on SPO11, of the single tyrosine conserved between the five homologues shows that this amino acid is essential for Spo11 activity. By analogy with the mechanism of action of known type II topoisomerases, we suggest that Spo11 catalyses the formation of double-strand breaks that initiate meiotic recombination in S. cerevisiae.

[Mechanisms and control of meiotic recombination in the yeast Saccharomyces cerevisiae]. / Mécanismes et contrôles de la recombinaison méiotique chez la levure Saccharomyces cerevisiae.

Recent studies in Saccharomyces cerevisiae have provided new insights in our understanding of the molecular mechanisms of meiotic recombination. Meiosis-specific DNA double-strand breaks have been detected and have been shown to be the lesions that initiate recombination events. These are located mostly in promoter regions where the chromatin is in an open configuration, and cluster in domains along the chromosome. They are likely to be made by a topoisomerase II-like protein encoded by the SPO11 gene. Several DNA intermediates in the meiotic double strand-break repair pathway have been characterised and several multi-protein complexes have been identified and shown to be involved at different steps in the repair pathway. The conservation of these protein complexes in higher eukaryotes suggests that the meiotic recombination mechanism could be conserved. With the application of the well characterised genetical, molecular, cytological and biochemical techniques and the recently developed technology for genomic studies (biochips), we can expect a rapid increase in our comprehension of the meiotic recombination process.