As people with HIV live longer lives on successful HIV treatment, their high risk for many cancers is an ever-increasing concern. Studies suggest that individuals living with HIV may be less likely to receive treatment for cancer than HIV-negative people. But to what extent are these differing rates driven by comorbidities, cancer type or other factors?
At AIDS 2016 in Durban, South Africa, I spoke with Anne F. Rositch, Ph.D., a cancer epidemiologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, whose research focuses on cancer in people living with HIV. Beyond simply raising the "'there's-a-disparity' flag," Rositch and her colleagues endeavor to take a broader view of the differences in rates of cancer treatment among older adults living with HIV versus the HIV-negative population.
Stay tuned to TheBodyPRO.com for a second interview with Rositch regarding her research on gynecological cancers in women living with HIV.
Welcome, Dr. Rositch. Tell us a bit about your research.
This is a population-level study, all in elderly adults -- our SEER-Medicare population. Everybody's over the age of 65, and as we know, an aging HIV population is becoming increasingly relevant.
There's some work in the general population in the U.S. that has shown that HIV-positive individuals are less likely to be treated for cancer. We looked at those rates in our elderly population because it helps us tease out which factors may be driven by HIV versus cost-benefit with regards to receiving treatment for cancer.
Unfortunately, with this type of data, we can't tease out the patients' or even the providers' perspectives, so we took a different approach by looking at some of the things that might make treatment medically contraindicated. There should be no direct effect of HIV on cancer treatment; it's really more of a marker of multiple, different things. That's what we're trying to sort out.
What kinds of variables did you look at in this study?
We looked at comorbidities as one of the things that might make the HIV population more or less likely to receive cancer treatment. We also looked at cancer stage -- we know our HIV population may have more advanced cancer at diagnosis -- to see if those factors would start to account for what we call an "HIV effect."
We had quite a large sample size: about 700 HIV-positive cancer patients. What we find, in general, is that people are getting treated. How we looked at treatment is by searching for billing codes that were specific treatment types for that cancer. While we know it's cancer-specific treatment, we don't necessarily know all of the nuances of that treatment. It's really just: Did they receive one of our four major types of treatment -- chemotherapy, radiation, surgery or a combination thereof?
Overall, we have 68% of our HIV-positive cases being treated for their cancer within a six-month timeframe, versus 75% treatment rates in the general population.
Just looking at the crude numbers, that is a statistical difference. We also think it's a substantive difference. We definitely want to close that seven percentage-point gap, but actually, it's also interesting that the 75% number is itself quite low. We think that is owing to the fact that this is an aging population.
When we look at the sample by age -- we have our "young-old" people [aged 65-70] and our "old-old" people [over the age of 70] -- we start to see things that are more pronounced. We actually see much more of a difference in treatment rates in the younger population. That's because, in the older population, a patient is just less likely to receive cancer treatment regardless of HIV status -- probably owing to their life expectancy drawing nearer; the clinical indications against treatment increasing, in general, with comorbidities; the inability of a given elderly individual to go into surgery; and things like that.
But in the 65- to 70-year-old individuals, 65% of the HIV-positive individuals are treated for their cancer, versus 81% in the HIV-negative population. What's interesting is the proportion goes down a little bit for our HIV-positive population, but it goes up a little [for our patients who are not living with HIV]. You really start to see the disparity in cancer treatment particularly in this younger age group. That's quite consistent with the literature that has focused more on younger populations.
We do see a lot of variability not just by age but also by cancer type. Treatment rates for some cancers -- bladder and breast, for example -- are just quite high, regardless of HIV or age. Melanoma is quite highly and equitably treated. Liver cancer, in general, has low treatment rates. But we definitely see both an age and an HIV effect.
Do the low rates of liver cancer treatment, for instance, have to do with the expected mortality rate for that type of cancer?
We can speculate as to why we're seeing differences by cancer. One of our next steps is to consult some of the specialists that treat these different cancers to get their perspectives: to find out if treatment for liver cancer is more invasive, or more fatal, or more complicated, or if life expectancy in general, given how individuals are diagnosed, is low, to try to understand those qualitative reasons. That won't be something that we can formalize, but the variability is really interesting.
Among those treated, in general we also see differences in time to treatment by HIV status. The HIV population is less likely [to receive treatment] and, among those who do, it takes longer -- a difference of about 14 or 15 days. That two weeks is a lot out of a six-month period. But there's also a different preparation of an HIV-positive individual to undergo these treatments. It's possible that it's actually in the HIV-positive patient's best interest. There could be beneficial reasons to have that delay -- something to do with their ART regimen, needing to get them up to a good level of health before they can undergo treatment. We, of course, want everybody to be treated and treated equally. But there may be reasons why these differences in time could actually indicate a better standard of care.
We're taking a more conservative approach to understand these differences instead of just touting the "there's-a-disparity" flag -- which is why we've used a different conceptual approach, and we're trying to really understand what part of this is HIV related, versus what is cancer related, and also the role of indications.
These final results here, the "fancy model" version of the raw data, are where we have adjusted for everything taking into account differences by race, gender, socioeconomic status and year of diagnosis. Those are ways in which we know that our HIV population may be different than our general population, and ways that may also affect treatment. We do still see that some cancers are less likely to be treated: HIV-positive individuals are clearly less likely to be treated for prostate cancer; same thing with kidney and colorectal cancers. But, in general, these variables we've included in the adjusted models, these underlying differences in the population, do account for some of the differences that we are attributing to HIV. The total effect here is that the gap has closed a little bit, compared with what we saw on a univariate, descriptive level.
This transcript has been lightly edited for clarity.
Coming soon: a second interview with Rositch regarding her research into gynecological cancers among women living with HIV.