Reviews of the literature  note that post-traumatic stress has been studied in a variety of cancers, including melanoma, Hodgkin lymphoma, breast cancer, and mixed cancers. The incidence of the full syndrome of post-traumatic stress disorder (PTSD) (meeting the full Diagnostic and Statistical Manual of Mental Disorders, fourth edition [DSM-IV], diagnostic criteria) ranges from 3% to 4% in early-stage patients recently diagnosed to 35% in patients evaluated after treatment. When incidence of PTSD-like symptoms (not meeting the full diagnostic criteria) are measured, the rates are higher, ranging from 20% in patients with early-stage cancer to 80% in those with recurrent cancer.
The earliest research (predating DSM-IV) on PTSD among survivors of cancer concentrated on the prevalence and characteristics of the disorder in patients who had been or were undergoing treatment, adult and child survivors of cancer, and/or the family members of these patients and survivors. A wide variety of cancer types were studied, including leukemia, breast cancer, and head and neck cancers. Much of the earlier research dealt with survivors of Hodgkin disease, probably because diagnoses at an early age and higher rates of survival resulted in a larger population available for study. These survivors were found to have a particularly high prevalence of intrusive thoughts and avoidance behaviors, even though they were many years posttreatment.[5,6,7] Most of these studies investigated PTSD-like symptoms, rather than the complete mental disorder with all diagnostic criteria.
By Darci Picoult
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The first study of cancer patients utilizing the current DSM-IV diagnostic criteria looked at 27 patients (mostly breast cancer), all at least 3 years postdiagnosis and no longer receiving any cancer treatments. In this study, a prevalence rate of 4% for current PTSD and 22% lifetime prevalence was found. Those who met criteria for lifetime prevalence were noted to have higher levels of general psychologic distress, suggesting that individuals with a history of PTSD are at a substantial risk for continued emotional difficulties.
Studies using the Structured Clinical Interview for DSM (SCID)  have found prevalence rates of PTSD between 3% and 10% in adult cancer patients. Most of these studies looked at women with early-stage breast cancer, evaluated a few months to a few years after their cancer treatments. Similarly, in a prospective study of 115 patients with all stages of breast cancer being treated in a comprehensive cancer center, 4% met the full diagnostic criteria for PTSD; 41% met the subsyndromal criteria for PTSD (experiencing intense fear, helplessness, or horror after being diagnosed with cancer). This set of subsyndromal criteria was a weak predictor of PTSD (12%) but an equally useful predictor of major depressive disorder, global anxiety disorder, and past major depressive disorder, and it may better serve as a marker for elevated distress. In a few studies of patients with bone marrow transplants, slightly higher prevalence rates have been reported, ranging from 5%  to 12% to 19%  to as high as 35%. The range in prevalence appears to be influenced by time of assessment (higher rates occurring with more time since transplant) and the assessment method used. Studies reporting lower rates typically used a self-report questionnaire, whereas those reporting higher rates  used the SCID and evaluated for symptoms at multiple times since diagnosis (i.e., lifetime prevalence).