Second Cancers That Follow Colorectal Cancer

With constant improvements in detection, diagnosis and treatment, the number of cancer survivors have increased significantly over the decades. While improved survival rates are encouraging not only to patients but also practitioners and researchers, an important caveat that may put a damper on things is the increased likelihood of developing a second cancer, something referred to as a second primary malignancy.

According to the Surveillance, Epidemiology, and End Results (SEER) program by the National Cancer Institute, classifying a cancer as an SPM is determined by five criteria:

1. Cancer site of origin: where the cancer is first detected.
2. Date of diagnosis: cancers that occur two months after diagnosis of the first cancer diagnosis are considered as SPMs unless it has been determined to be recurrent or metastatic.
3. Histology: the microanatomy of tumor cells and tissues as seen through a microscope
4. Tumor behavior: if it remains localized or has metastasized
5. Laterality of paired organs: paired organs are organs where there are two of each kind, e.g. lungs, breasts, kidneys, ovaries and testes. Each organ in the pair is considered separately and described as lateral unless the cancer is determined as found in both sides. In the latter case, it is considered bilateral.

At present, cancer patients are at 20% risk of being diagnosed with a new primary cancer, and this risk increases to 30% in cancer survivors over 60 years old. On one hand, colorectal cancer is a commonly occurring second cancer due to various risk factors that are often present in other cancers. On the other hand, colorectal cancer can also increase the risk of other primary cancers developing.

As it stands, various retrospective cohort studies have identified different SPMs that colorectal cancer patients are likely to develop. While there is some variation to the cancers that have been identified, most studies consistently singled out the following second cancers in colorectal cancer survivors.

• Colorectal cancer (Non-recurring or metastatic cancer; new primary malignancy)
• Breast cancer
• Prostate cancer
• Lung and bronchus cancer
• Urinary bladder and kidney cancer

While it varies from cancer to cancer, the risk of developing the different SPMs are frequently associated with lifestyle, environmental exposure to carcinogens, existing medical conditions and hereditary syndromes such as familial adenomatous polyposis (FAP) or Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC).

Age also made a significant difference. Patients aged 65 and above were approximately two times more likely to develop SPM compared to patients below 45 years old, and most SPMs were found to develop between 0 to 5.2 years after the initial colorectal cancer diagnosis, with the likelihood increasing the more time has passed after the first diagnosis.

Experts constantly cite awareness as being key in preventive healthcare, but the same also applies to surveilling cancer survivors for SPMs. This is due to the poor prognosis for patients diagnosed with SPMs after colorectal cancer, which is also worse than those who are diagnosed with just colorectal cancer, and ultimately result in higher mortality rates in patients with SPMs.

The lethality of the SPMs — especially for lung or liver cancers — is thought to be one of the reasons for a worse prognosis. Patients who also previously received chemotherapy or radiation therapy are also less likely to respond well to repeat treatments. With age also being a major influential factor, patients diagnosed with SPM are likely to be older compared to their first colorectal cancer diagnosis, and are less resilient to tolerate aggressive chemotherapy or radiation treatments. Above all, being diagnosed with cancer a second time will surely have a negative psychological impact — of which the ties to overall survival are directly correlated.

What then, can be done to improve the chances of survival for patients who have already been through the difficulties of treating and surviving colorectal cancer the first time?

On one hand, regularly screening and monitoring the health of these patients can increase the likelihood of detecting any second cancers early. On the other hand, many of the standard screening procedures are often more costly, though they boast a better track record of more accurate detection of cancerous lesions. Making use of inexpensive and non-invasive screening methods can ease this financial barrier and help establish regular screening programs for these high-risk individuals. Ultimately, managing the different risk factors of each likely SPM and constant surveillance are still the best ways to improve the chances of survival.