Review by Curtis May
Despite the increased longevity breast cancer surgery provides patients, 25-60% of patients are expected to experience persistent post-surgical pain. An updated systematic review of the evidence was done to identify the main predictors of developing chronic pain following breast cancer surgery and then how to reduce this risk.
I chose this article for two reasons
- It’s on the topic of early intervention: prevention of chronic post-surgical pain, extremely important and cost effective.
- It was published from the Michael Degroote National Pain Research Centre, a place I have been working with (casually) for the last 1.5 years!
Wang L, Guyatt GH, Kennedy SA, Romerosa B, Kwon HY, Kaushal A, et al. Predictors of persistent pain after breast cancer surgery: a systematic review and meta-analysis of observational studies. Canadian Medical Association Journal. 2016;188(14):E352–E361.
The authors systematically searched the literature for all relevant studies that explored risk factors in developing persistent pain following breast cancer surgery. They screened articles for quality and combined their data to conduct a “meta-analysis”, an analysis of combined data from multiple similar studies. Meta-analyses allow us to make more confident conclusions about how well a treatment or preventive strategy works by combining all related studies around a topic into one giant study. This study ended up including 30 studies in the final analysis. Among the 30 studies, persistent pain was defined as pain lasting at least 3 months following surgery (range 3.28-72.50 months).
The study calculated a baseline risk of persistent post-surgical pain to be 30% of patients who underwent surgery. This study assessed 9 predictors that were thought to increase the risk of persistent pain following surgery. Of those 9 predictors, when pooled together in this meta-analysis, it was found that younger age, use of radiotherapy, axillary lymph node dissection (where they take multiple lymph nodes surrounding the breast tissue out), greater acute postoperative pain levels, and the presence of pre-operative pain predicted increased incidence of persistent post-operative pain. In contrast, BMI, the type of breast cancer surgery, use of chemotherapy, or use of endocrine therapy did not predict persistent post-operative pain. Of significance, the use of axillary lymph node dissection as opposed to sentinel lymph node dissection (where they only take out the primary lymph node) was the most predictive of persistent post-surgical pain relative to all 9 predictors, with an absolute 21% increased risk! This is compared to age, the next most predictive factor, which predicts a 7% increased absolute risk of developing persistent pain with each ten-year decrement of age.
Given that axillary lymph node dissection is the most predictive of persistent post-surgical pain, the authors recommend modifying surgical techniques used to perform axillary node dissections to reduce the risk of persistent post-surgical pain. These modifications may include use of sentinel lymph node dissection instead, or active preservation of the intercostobrachial nerves during axillary lymph node dissection to reduce accidental nerve damage. As for the other predictors, such as young age, it may be indicated to selectively target these cohorts of patients to reduce their risk of developing persistent pain by controlling pain levels before and after surgery, or providing preventive therapy such psychotherapy if indicated.
One could say that the reliance on observational study design, such as cohort studies, increased the risk for bias. However, all studies were found to be of low risk for bias. Use of observational designs may also reduce the ability to infer causality. However, chronic post-surgical pain is complex and is difficult to capture the complexity through an experimental design, also with challenging ethical considerations. One limitation that the authors identified was that some of the studies included did not make it clear whether they excluded previously existing chronic pain states, or if they were measuring newly diagnosed chronic post-surgical pain. Thus, rates of persistent post-surgical pain may be overestimated.
At CHANGEpain, the foundational therapies offered through CHANGEpain’s Together Group Programs are broadly effective interventions to reduce the risk of persistent post-surgical pain. It should be that similar strategies are adopted for at risk surgical patients in the hospital, in addition to specific modifications such as surgical technique to reduce the incidence of persistent post-surgical pain, not limited to breast cancer surgery.