Type of study: Four nested case-control studies using a large population-based electronic medical records database

The finding: There is no statistically significant association between PTSD and risk for lung, breast, prostate or colorectal cancer.

Strength and weaknesses: Among the strengths is the access to a large UK database with almost 12 million individuals, which allowed for large samples for each case-control. The group made an effort to address potential medical confounders such as obesity and smoking history, and to stratify cases by use of antidepressants. It also does an excellent job of reviewing the existing literature and giving context to their findings concerning those of previous studies. As for weaknesses, the PTSD prevalence was lower than the average for the UK, and this may be associated with PTSD being underdiagnosed in a primary care setting. Other weaknesses are those associated with these type of studies, for instance, the
necessary information may have been unavailable, the researcher did not do data collection, additional confounders were not included (e.g., family history of malignancies), missing information on data quality, truncation at start of follow-up, making it difficult to differentiate between prevalent and incident cases.

Relevance: There are two main points. First, it adds to the limited but growing literature between the effects of trauma and stress as a risk/no risk for cancer; the large sample and straightforward results can help strengthen our education and help address myths and fears common among patients with cancer. Second, it highlights the benefits of using database and patient registries as a powerful tool to help answer questions for which conducting prospective studies demands hard to meet challenges.

Type of study: Systematic literature review

The finding: In patients who have received a stem cell transplant as a treatment for a hematologic malignancy, positive psychological constructs appear to be associated with improved quality of life and function as well as reduced rates of depression and anxiety.

Strength and weaknesses: Among the strengths of this review is the number of studies included and the total sample size. Also, the authors analyze the impact of optimism across different domains (quality of life, the incidence of depression, anxiety and PTSD, and medical outcomes). Another strength is the conceptual model presented that illustrates the relationship between biological, psychological, behavioral factors with positive psychology constructs and stem cell transplant outcomes. Among the weaknesses for this manuscript are those associated with the limitations of the included studies, for instance, limited race diversity among participants, US-centric results, restrictions imposed by individual study designs. Finally, it focuses mainly on optimism and did not include other constructs such as spirituality, self-efficacy or social support which could have further strengthened the results.

Relevance: This study it is the first to assess the associations between positive psychology constructs and health outcomes in patients with hematological malignancies post-HSCT, giving solid strength to argue in favor of implementing these cost-effective interventions early in the process.

Type of study: Systematic review

The finding: The authors conducted a systematic review and meta-analysis of whether psychological interventions can impact inflammatory biomarkers (e.g., IL-6, CRP, TNF-alpha, IL-1beta) in the medically ill (7 of 19 studies were comprised of cancer patients). They found that psychological interventions had a statistically significant but small effect on lowering inflammatory biomarkers—mostly CRP—which did not persist at the time of follow up. Among the few studies that pre-selected patients with higher distress, there was a nonsignificant trend towards psychological interventions having a greater effect.

Strength and weaknesses: The authors used solid methodology to conduct their review, and drew on previous literature to tailor their inclusion and exclusion criteria. For example, they excluded studies that had >50% physical activity because physical activity is known to impact inflammatory markers. In turn, the authors reported low statistical heterogeneity between the studies they included, which suggests that their findings likely reflect actual findings rather than chance. The authors included a number of moderation analyses to study whether the effects of known potential confounding variables were significant. The limitations of the study mostly reflect the limitations of the individual studies that were included. For example, most studies did not include a follow-up analysis. In addition, not all studies controlled for time of sampling, only samples once per time point, or controlled for differences between blood samples and saliva samples of biomarker.

Relevance: Because of widely held beliefs linking stress and cancer, patients with cancer often look towards stress reduction as an imperative. Some even do so with such intensity that they risk increasing their stress by worrying about their worrying. This systematic review seems to suggest only a small, if any, benefit of psychological interventions on lowering inflammatory biomarkers in patients with cancer, reflecting a common belief among some psycho-oncologists that investing greater effort in stress reduction yields diminishing returns. The study does suggest, however, that there might be a subset of patients—those with the greatest distress—who potentially reap the greatest reduction in inflammatory biomarkers following psychological interventions, and further studies will need to explore this further. For now, psycho-oncologists can use this study to try and reassure their patients that while psychological interventions are effective for a number of outcomes, lowering inflammatory biomarkers in a robust way does not seem to be one of them.