Acquired Resistance to Activated Protein C (aAPCR) Is Associated with Increased Risk of Deep Vein Thrombosis in Multiple Myeloma.

Non factor V Leiden APC resistance (aAPCR) has been described in cancer patients and found to be associated with an increased risk of deep venous thrombosis (DVT). We analyzed the incidence and clinical impact of APC resistance in a large group of multiple myeloma patients. A total of 1178 myeloma patients were tested for APC resistance using an aPTT-based assay in the presence of excess of factor V-deficient plasma and the ratio with or without APC was calculated (≤ 2.00 was considered abnormal). PCR amplification of genomic DNA was used to detect Factor V Leiden.

Abnormal APC resistance was found in 109 patients (9.3%), 83 of those were tested for factor V Leiden, 31 had the mutation and 52 (63%) did not have it. Analyzing a subgroup of 254 chemotherapy naïve patients, APC ratio was abnormal in 11% of patients and two third of them were not carriers of factor V Leiden mutation. The presence of aAPC resistance was associated with an increased risk for DVT: 27.9% in patients with aAPCR vs.12.3% in the others (P = 0.008); 22.6% in patients with factor V Leiden mutation.

In 32 patients with abnormal aAPCR, the test was repeated: 31/32 patients normalized their APC ratio in sequential testing. Correlation between myeloma baseline markers (serum and urine M-component, beta2-microglobulin, CRP, IL-6), response to treatment and APC activity were studied. In this analysis active disease emerged as the most important factor associated with aAPCR, as 19 patients with normalization of the APC ratio had a concomitant clinical response to therapy. We concluded that aAPCR is a transient finding in myeloma patients that showed a significant correlation with development of DVT.