A new study in the European Journal of Cancer has confirmed the key importance of heredity (i.e., genetic inheritance) as one of the risks for prostate cancer and two other common forms of cancer (breast and colorectal cancers).
Zöller et al. used data compiled in the The Swedish Multi-Generation Register to follow all adopted children in Sweden born between 1932 and 1969 for a diagnosis of any one of the three above-mentioned cancers — between January 1, 1958 and December 31, 2010. They were also able to
- Estimate risk for the same three cancers in adoptees with at least one biological parent with the same cancer type compared with adoptees without no biological parent with the same cancer type
- Determine risk for the same three cancers in adoptees with at least one adoptive parent with cancer compared with adoptees with no adoptive parent with cancer
Here are the core findings of the study:
- The total number of adoptees tracked in the study was 70,965.
- Compared to adoptees with no known biological parents with a cancer of the same type, the incidence of cancer among adoptees with at least one biological parent with a cancer of the same type (using the standardized incidence ratio or SIR) was
- 1.8 for prostate cancer
- 2.0 for breast cancer
- 1.9 for colorectal cancer
- Compared to adoptees with no known biological parents with a cancer of the same type, the incidence of cancer among adoptees with at least one adoptive parent with a cancer of the same type (again using the standardized incidence ratio or SIR) was
- 1.2 for prostate cancer
- 0.97 for breast cancer
- 1.1 for colorectal cancer
- In other words, adoptees with at least one adoptive parent with prostate, breast or colorectal cancer (but no biological parent with a cancer of the same type) were at no significantly increased risk of these respective cancer types.
The findings from this study clearly demonstrate that genetic and/or biological factors are of real significance in risk for familial transmission of prostate, breast, and colorectal cancer. However, as Dr. Zöller was very quick to note in an associated media release from Lund University:
The results of our study do not mean that an individual’s lifestyle is not important for the individual’s risk of developing cancer, but [they do suggest] that … risk for the three most common types of cancer is dependent to a [significant] extent on genetics.
The bottom line seems to be that (at least in the Swedish population) risk for one of these three common cancers among adoptees with at least one biological parent who had had the same cancer is about 80 to 100 per cent higher than for a control group with no biological parent with the same cancer.
Apparently, in the full text of the paper, there are also data suggesting that:
- Individuals with a biological parent with cancer also developed the disease at a younger age than those without a biological parent with the same cancer.
- The age at which an individual developed cancer was not affected by whether an adoptive parent had had the same cancer.
As Dr. Zoller also points out in the media interview
The occurrence of breast cancer, prostate cancer and colorectal cancer in biological parents is an important risk factor that should be included in patients’ medical history and examinations. It is therefore important that doctors ask about family history so that they can decide whether further tests are needed.
It is, of course, important to place the clinical significance of such risk in context.
Clearly a young man whose father is diagnosed with low-risk prostate cancer in his early 70s, and whose father dies in his mid-80s of something other than prostate cancer after 15 or so years on some form of expectant management, has a very different type of future “risk” from prostate cancer than an otherwise similar young man whose father was diagnosed with aggressive, high-risk prostate cancer in his late 50s and who dies 20 years later of metastatic prostate cancer after a series of treatments. In other words, it is not enough for the primary care physician to just not “Fam. Hx prostate cancer” in the patient’s notes — the Devil is going to be in the details (assuming that at least some of these are known).