Preoperative Thrombocytosis Predicts Shortened Survival in Patients with Malignant Peritoneal Mesothelioma Undergoing Operative Cytoreduction and Hyperthermic Intraperitoneal Chemotherapy.

BACKGROUND: This study was designed to determine the clinical significance of preoperative thrombocytosis in patients with malignant peritoneal mesothelioma (MPM) undergoing operative cytoreduction (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). CRS and HIPEC have been associated with prolonged survival in patients with MPM and is the preferred treatment in select patients. However, patient selection criteria remain ill-defined for this operation that is also associated with significant morbidity and mortality. Preoperative thrombocytosis has been associated with poor outcomes in various malignancies but never studied in MPM. METHODS: Between January 2006 and December 2015, 100 patients with high-grade epithelioid MPM were evaluated and selected for CRS and HIPEC at our center (M: 53, F: 47; mean age: 54 years [range 17-81 years]). We analyzed various patient and treatment related factors potentially associated with overall survival (OS). RESULTS: The median actuarial overall survival was 32.8 months; the actuarial 1-, 3-, 5-year survivals were 70, 49, and 36%, respectively. On multivariate analysis, suboptimal resection (CCR > 1), high tumor burden (PCI > 20), and elevated preoperative platelet count (>367,000/mm3) were independently associated with shortened OS (P < 0.05). Median OS in patients with elevated versus normal platelet counts were 13 and 58 months, respectively (P < 0.001). Compared with patients with normal platelet counts, patients with elevated counts had significantly greater residual disease after operation (P = 0.008). CONCLUSIONS: Elevated preoperative platelet count is independently associated with poor outcome. Notably, thrombocytosis reflects aggressive tumor biology and should be considered a factor in patient selection for CRS and HIPEC.

RNA∶DNA hybrids initiate quasi-palindrome-associated mutations in highly transcribed yeast DNA.

RNase H enzymes promote genetic stability by degrading aberrant RNA:DNA hybrids and by removing ribonucleotide monophosphates (rNMPs) that are present in duplex DNA. Here, we report that loss of RNase H2 in yeast is associated with mutations that extend identity between the arms of imperfect inverted repeats (quasi-palindromes or QPs), a mutation type generally attributed to a template switch during DNA synthesis. QP events were detected using frameshift-reversion assays and were only observed under conditions of high transcription. In striking contrast to transcription-associated short deletions that also are detected by these assays, QP events do not require Top1 activity. QP mutation rates are strongly affected by the direction of DNA replication and, in contrast to their elevation in the absence of RNase H2, are reduced when RNase H1 is additionally eliminated. Finally, transcription-associated QP events are limited by components of the nucleotide excision repair pathway and are promoted by translesion synthesis DNA polymerases. We suggest that QP mutations reflect either a transcription-associated perturbation of Okazaki-fragment processing, or the use of a nascent transcript to resume replication following a transcription-replication conflict.

Two distinct mechanisms of Topoisomerase 1-dependent mutagenesis in yeast.

Topoisomerase 1 (Top1) resolves transcription-associated supercoils by generating transient single-strand breaks in DNA. Top1 activity in yeast is a major source of transcription-associated mutagenesis, generating a distinctive mutation signature characterized by deletions in short, tandem repeats. A similar signature is associated with the persistence of ribonucleoside monophosphates (rNMPs) in DNA, and it also depends on Top1 activity. There is only partial overlap, however, between Top1-dependent deletion hotspots identified in highly transcribed DNA and those associated with rNMPs, suggesting the existence of both rNMP-dependent and rNMP-independent events. Here, we present genetic studies confirming that there are two distinct types of hotspots. Data suggest a novel model in which rNMP-dependent hotspots are generated by sequential Top1 reactions and are consistent with rNMP-independent hotspots reflecting processing of a trapped Top1 cleavage complex.

Mutagenic processing of ribonucleotides in DNA by yeast topoisomerase I.

The ribonuclease (RNase) H class of enzymes degrades the RNA component of RNA:DNA hybrids and is important in nucleic acid metabolism. RNase H2 is specialized to remove single ribonucleotides [ribonucleoside monophosphates (rNMPs)] from duplex DNA, and its absence in budding yeast has been associated with the accumulation of deletions within short tandem repeats. Here, we demonstrate that rNMP-associated deletion formation requires the activity of Top1, a topoisomerase that relaxes supercoils by reversibly nicking duplex DNA. The reported studies extend the role of Top1 to include the processing of rNMPs in genomic DNA into irreversible single-strand breaks, an activity that can have distinct mutagenic consequences and may be relevant to human disease.