Ultrasound screening of cancer patients judged to be at high risk for venous thromboembolism (VTE) can identify a significant number of deep vein thrombosis (DVT) cases, according to research from the University of Rochester Medical Center.
In a prospective study, three (9%) of 32 high-risk patients had asymptomatic DVT at baseline ultrasound screening, according to the researchers. An additional case was detected during a subsequent serial ultrasound exam.
"In this high-risk patient population, screening ultrasonography for asymptomatic thrombosis may be of value in early detection and treatment of asymptomatic DVT," said Dr. Katherine Kaproth-Joslin, PhD.
She shared the team's findings during a session at the recent American Institute of Ultrasound in Medicine (AIUM) annual meeting.
VTE is a common complication linked with malignancy and antineoplastic therapy, Kaproth-Joslin said. Cancer increases the risk of thrombus by four times over the general population, and starting chemotherapy increases the thrombus rate by six times. Furthermore, cancer patients with VTE have two times the mortality rate of patients without thrombus, she said.
Prophylaxis comes with the risk of bleeding, the cost of the medication, and the risk of developing heparin-induced thrombocytopenia. However, primary prophylaxis has been shown to reduce DVT and pulmonary embolism (PE) in high-risk populations such as postoperative and acutely ill hospitalized patients, she said.
A risk-score model developed by Khorana et al (Blood, May 15, 2008, Vol. 111:10, pp. 4902-4907) for VTE stratifies cancer patients based on five clinical and laboratory factors: site of cancer, platelet count, hemoglobin levels, leukocyte count, and body mass index (BMI).
Screening utility
In their study, the University of Rochester researchers sought to assess the utility of screening for thrombosis in a prospective cohort of initially asymptomatic cancer patients who were starting outpatient chemotherapy.
Patients were included if they were adults with a new diagnosis of cancer and were scheduled for a minimum of three cycles of outpatient chemotherapy. Individuals also had to be at high risk for developing VTE, with a risk score of 3 or greater. Those with a prior history of VTE were excluded, as were those who were receiving ongoing anticoagulation or prior chemotherapy for the current cancer diagnosis, according to the group.
Of the 35 patients included in the study, 32 were screened with baseline ultrasound of the bilateral lower extremities before the start of chemotherapy. Ultrasound was performed approximately every four weeks after each chemotherapy cycle. In addition, imaging exams obtained for restaging purposes or for symptomatic VTE events were also evaluated for clots, Kaproth-Joslin said.
The rates of VTE in high-risk patients were as follows:
- All types of VTE: Eight patients (23%)
- DVT: Five patients (14%)
- Both DVT and PE: Two patients (6%)
- PE: One patient (3%)
Three (9%) of the 32 patients were diagnosed with VTE at baseline ultrasound. One was diagnosed at the week 12 ultrasound scan.
In addition, two patients developed symptomatic DVT between weeks 1 and 4 after initiation of chemotherapy. Restaging CTs also identified two asymptomatic PEs at weeks 6 and 9, after initiation of chemotherapy; one of these became symptomatic a week later, according to the researchers.
Variable in nature
The location and extent of clots varied, Kaproth-Joslin said. Thrombus distribution was as follows:
- PE with DVT: 25%
- Unilateral calf: 25%
- Unilateral calf and thigh: 25%
- PE: 12.5%
- Unilateral upper extremity: 12.5%
Fifty percent of patients with VTE had a calf clot, and half of these had a unilateral clot, she said.
High-risk cancer patients develop thrombus at much higher rates than the general population, Kaproth-Joslin noted. Twenty-three percent of the patients in the study developed thrombosis, compared with published rates of 0.05% in the postoperative population and 5% to 7% in the acutely ill hospitalized population, she said, while 9% of high-risk patients had asymptomatic DVT at baseline screening.
"The risk score is valid and highly predictive of identifying patients at risk for VTE," she said. "Screening ultrasonography for asymptomatic thrombosis should be considered in high-risk patients based on this risk score."
In addition, the study showed that it's important to screen for VTE in the calf, Kaproth-Joslin said. Of the high-risk patients with VTE, 50% had a calf clot and were subsequently treated.
"This region should be included in the assessment of DVT," she said.
