Antidepressant adherence and cancer survival

The whole topic of cancer and depression and the value of antidepressants is large and sometimes contested and uncertain. Some studies suggest that depression is under-diagnosed in cancer patients (meaning that more people actually are clinically depressed than are diagnosed that way) while others indicate that depression is more common among cancer patients than the general population. Whenever I think about this, I come back to a few basic thoughts:

• If someone thinks that she is depressed, she should be taken seriously. We know ourselves well.
• Of course just about everyone with cancer is sometimes sad or scared. These feelings are normal and not the same thing as depression.
• It takes an experienced and skilled clinician to ferret out true depression, the kind that will be relieved with medication, from the normal reactions to having a potentially life-threatening illness.

I have been thinking about this since learning of a recent large cohort study of Israeli cancer patients. The report is that antidepressant adherence above 50% was associated with one quarter less mortality over four years when compared with adherence below 20%. This is tantalizing, indeed, but there are so very many variables that must influence the results. Let's start here: Correlation is not causation.

And then let's continue here: Generally speaking, people who comply with recommended treatment likely comply both with treatment for cancer and treatment for depression. People who took regular medication for depression probably also took regular anti-cancer medications as prescribed. They may also have different life styles in a broader context. Perhaps people who complied with anti-depressants also went to the gym and drank less alcohol and had more friends. Coming at it from another perspective, we don't know the severity of depression of people in the study, and we don't even know if they actually were depressed. It is certainly possible that some, see the first paragraph here, were reacting to a difficult diagnosis and treatment and didn't need or benefit from antidepressants at all.

And there are the important factors of insurance and cost. Maybe people who didn't stick with the antidepressants had insurance that did not cover the full cost. If money is tight, it can be tough to choose how best to spend it, and medication might not be the first choice. We know that many cancer patients don't take as much medicine as prescribed because of cost. They may take a pill once a day instead of twice or every other day instead of daily. It seems likely that people would do the same with antidepressants.

I am reminded of an old study that found that 92% of non-depressed woman accepted and complied with adjuvant treatment for breast cancer while only 50% of depressed women did so. Right there we have a possible confounding variable.

So, what could we take away from this Israeli study? First, I am gratified that attention is being paid to mental health issues for people going through cancer. It is very difficult and stressful to manage cancer treatment, and coping with a simultaneous depression or other mood disorder or psychological problem makes it much harder. It is good practice to always ask how someone is feeling and coping. As patients, we are regularly weighed and measured and asked about pain. Asking also about mood or distress is important, too. We can also remember that any study, no matter how good it is, may raise as many questions as it answers.