A diagnosis of prostate cancer raises understandable concerns about overall health and the future risk of other malignancies. When considering the risk of a new cancer in a prostate cancer survivor, it is important to distinguish between metastatic disease (the spread of the original cancer) and a second primary cancer (a completely new and separate tumor). Surveillance for new cancers becomes a significant part of long-term care for survivors. This is because treatment for the first cancer and shared risk factors can influence the development of a second malignancy. This topic is relevant as improved treatments mean prostate cancer survivors are living longer.
Understanding the Risk of Second Primary Cancers
Men who have been treated for prostate cancer often have a lower overall risk of developing a second primary cancer compared to the general male population. This is largely because the initial diagnosis leads to increased medical surveillance. However, this generalized lower risk does not apply universally, and a measurable increase in risk is noted for certain malignancies.
This increased risk is quantified using the Standardized Incidence Ratio (SIR). The SIR compares the observed number of new cancers in prostate cancer survivors to the expected number in the general population. While the overall SIR may be less than one, the SIR for certain cancers is greater than one. Cancers of the bladder, kidney, endocrine, and soft tissues are generally found to have a greater risk following a prostate cancer diagnosis.
The strongest associations are observed for cancers near the prostate, such as the bladder and rectum, particularly after certain treatments. While a relative risk increase exists for these specific cancers, the absolute risk remains low for most individuals.
Common Causes Predisposing Both Cancers
The development of both prostate cancer and a second cancer is often rooted in shared susceptibility factors. The single most significant factor linking prostate cancer and other malignancies is increasing age, as cancer risk naturally rises as the body accumulates genetic damage over a lifetime. Shared lifestyle components, such as obesity and a history of smoking, also contribute to both prostate cancer risk and the risk of various other cancers, including lung and colorectal tumors.
Genetic predisposition plays a substantial role in linking prostate cancer to other malignancies through inherited mutations in DNA repair genes. Mutations in BRCA1 and BRCA2 genes, famously associated with breast and ovarian cancers, also increase the risk of developing prostate cancer. Men with a BRCA2 mutation face a significantly elevated risk of prostate cancer that tends to be more aggressive and diagnosed at a younger age.
Another significant genetic overlap is seen with Lynch syndrome, which is primarily known for increasing the risk of colorectal and endometrial cancers. Men with certain Lynch syndrome mutations are also predisposed to an aggressive form of prostate cancer. Understanding these shared genetic pathways highlights why a history of prostate cancer may warrant screening for other cancer types, as the underlying genetic defect increases the risk for multiple primary tumors.
How Prostate Cancer Treatment Impacts Future Risk
Curative interventions for prostate cancer can introduce a new risk factor for developing a second primary cancer years after the initial treatment.
Radiation Therapy
Radiation therapy uses high-energy beams to destroy cancer cells. This can cause secondary tumors in adjacent, non-cancerous tissues due to localized radiation exposure. This risk is primarily confined to organs near the prostate, such as the bladder and the rectum.
Radiation-induced second cancers have a latency period, typically appearing five to fifteen years after the initial treatment. The increased relative risk for bladder cancer and rectal cancer following external beam radiation therapy is consistently observed in long-term studies. Newer radiation techniques, such as intensity-modulated radiation therapy, aim to reduce the dose to surrounding healthy tissues. The theoretical risk remains a consideration, particularly for younger patients with a long life expectancy.
Androgen Deprivation Therapy (ADT)
Androgen Deprivation Therapy (ADT), a hormonal treatment that lowers male hormone levels, has systemic effects that may also influence the risk of other cancers. ADT can lead to metabolic changes, including changes in body composition and an increased risk of diabetes. These factors are known to be associated with cancer development. The evidence regarding ADT’s link to specific secondary cancers is complex and sometimes contradictory, with some studies suggesting a higher overall risk of secondary cancers, while others find a lower risk for certain cancers like those of the liver or lung.
The increased medical follow-up that prostate cancer survivors receive can also contribute to the detection of second primary tumors. This surveillance bias means that even if a second cancer is biologically unrelated to the prostate cancer or its treatment, it is more likely to be found earlier because the patient is undergoing frequent testing and screening.