Q&A: Explaining early-stage cancer prognoses using survival rates
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Physicians may use disease-specific or relative survival rates to explain a prognosis to patients with early-stage cancer, but both types of survival rates have limitations, according to a study published in JAMA Internal Medicine.
Disease-specific survival (DSS) rates describe the proportion of patients who did not die from their cancer in a specific time frame, whereas relative survival (RS) rates compare the survival of individuals with people from a similar population who do not have cancer, and they account for patient characteristics like smoking history.
In their study, researchers calculated both types of survival rates for patients with early-stage cancers, and they found that RS rates were higher than DSS rates for five early-stage cancers — prostate cancer, ductal carcinoma in situ, stage I melanoma, stage I thyroid cancers, and breast cancer — and even suggested that these patients were likely outliving similar individuals without cancer.
Luc G. T. Morris, MD, MSc, FACS, a surgeon at Memorial Sloan Kettering Cancer Center, spoke with Healio Primary Care about the pros and cons of each approach to calculating survival, and how the findings support active surveillance as a reasonable treatment option for certain cancer types. – by Erin Michael
Q: What are the strengthens and limitations of relative and disease-specific survival rates in early-stage cancers?
A: They each have pros and cons. Ultimately, patients want to understand their “net survival” rate, which is the rate of survival isolated to the cancer, not including other causes of death. DSS can show this but it is not a very intuitive measure — it is the measure of the probability of not dying of cancer, which may be hard for patients to understand. RS probably is the most intuitive concept for patients to understand — they want to know how the cancer diagnosis altered their survival, relative to someone like them who does not have cancer.
Q: Should physicians use DSS or RS rates when determining a patient’s prognosis?
A: Both DSS and RS get at this concept of helping patients understand their net survival. Ideally, physicians should have a sense of each of these numbers — usually they are the same number. But in some cases, RS will be different from DSS, because the cancer population is not perfectly comparable to a matched noncancer population. These are cases that can illuminate particularities about some types of cancer. For example, patients with lung cancer will have RS that is worse than DSS, because they are more likely to be smokers, and smokers have higher all-cause mortality. In this paper, we found that there are cancers that are probably associated with patients who are healthier, and more health conscious, than comparable patients without the cancer diagnosis. This is because these types of cancer are cancers that have high rates of survival because they are prone to overdiagnosis, and that the diagnosis of these cancers is a reflection of the fact that the patients tend to seek out preventive care and engage in other healthy activities.
Do RS rates help patients understand their prognosis?
We hope these types of statistics help to explain to patients that, at least for these five types of cancer, their actions and their lifestyle prior to their cancer diagnosis are probably more important to their prognosis than the cancer diagnosis itself.
Patients receiving a cancer diagnosis are susceptible to incredible anxiety and even higher rates of depression, which are both very understandable when you imagine that the word cancer implies that their survival has been compromised. We hope that these statistics help patients with these types of cancer understand that indeed these cancer diagnoses do not imply they will have impaired survival. In fact, it may mean the opposite — not because the cancer diagnosis makes them live longer, but because the diagnosis reflects attentiveness to health.
You mentioned in your research letter that survival rate statistics can “open the doors to considering active surveillance.” Can you explain?
Active surveillance is an approach that is well-suited for cancers prone to overdiagnosis, such as these. It is well accepted for prostate cancer, now being introduced for thyroid cancer, and being investigated in a large randomized controlled trial for ductal carcinoma in situ. Many patients at first may be concerned about not having surgery or radiation treatment for a cancer that might have compromised their survival. These statistics help to explain why active surveillance is a reasonable approach — they show that these cancer diagnoses often do not mean poorer survival, and in fact, may be associated with patients who are likely to have excellent survival, possibly even better than comparable patients without the cancer diagnosis.
Reference:
Marcadis AR, et al. JAMA Intern Med. 2019;doi:10.1001/jamainternmed.2019.6120.
Disclosure: Morris reports research funding (no personal payments) from AstraZeneca, Bristol-Myers Squibb and Illumina unrelated to this work.