Sir Spheres for Liver Metastases from Prostate Cancer

BY MARK SCHOLZ, MD

Cancer that spreads outside the prostate gland is what makes prostate cancer dangerous. Metastatic prostate cancer cells cause malfunction by impeding normal function. Some organs, like lymph nodes for example, continue to function quite nicely, even if the degree of cancer spread is extensive.  Lymph node spread, therefore, is the least dangerous form of prostate cancer metastases.  At the other end of the spectrum is the liver, which is far less tolerant.  The seriousness of bone metastases, the most common site of prostate cancer spread, lies about half way between that of node metastases and liver metastases.


The earliest stages of metastases are microscopic and therefore invisible even with the best available technology. To be detected with the best available PET scan technology, small tumors must measure more than 1/8 of an inch across. For detection with standard CT scans and MRI scans, more than a half-inch sized tumor is necessary. Since the presence of metastases is such a defining issue when describing a cancer’s character, men who are newly-diagnosed are labeled as low, intermediate or high-risk depending on their estimated likelihood of micro-metastatic disease. Liver metastases are extremely rare at the time of initial diagnosis of prostate cancer. When they occur it is usually after many years of ongoing treatment for known metastatic disease in the bone.


Prophylactic treatment with hormone therapy, chemotherapy or radiation to treat the possibility of micro-metastases is common for high-risk prostate cancer and occurs maybe half the time in intermediate-risk prostate cancer. The goal is to cure the micro-metastases at an early stage when they are most susceptible to eradication, thus preventing the future development of detectable metastases which is what makes cancer life threatening.


When talking about prostate cancer, even though this is a blog about metastases, it should always be remembered that many common types of prostate cancer never spread. These low grade “cancers” are genetically distinct and represent a totally different category of disease.  However, when discussing the type of prostate cancer that is capable of metastasis, the following factors impact how dangerous it is:

1. The site of spread.
2. The extent of spread
3. The tumor cell growth rate
4. The efficacy of available treatment

As noted above, the liver is far less tolerant to metastatic invasion than bone or lymph nodes.  In addition, because liver metastases tend to occur in men with advanced disease, tumor growth rates tend to be brisk. Also, the most commonly administered treatments, hormone therapies and chemotherapy, have often already been tried before liver metastases first develop. The advent of liver metastases, therefore, usually represents a very serious and life threatening issue.


Liver metastases may first be suspected when standard blood tests such as ALT, AST or ALP which are components of a hepatic panel blood test, register outside the normal range. Investigation into their cause often leads to doing a CT scan or MRI scan of the abdomen and pelvis to confirm the presence of disease in the liver. Alternatively, a scan may detect abnormal spots in the liver during routine periodic scanning that is being performed as regular surveillance.


Hormone therapy with Lupron, Zytiga and Xtandi, or chemotherapy with Taxotere, Jevtana and Carboplatin, is the standard approach to treatment for liver metastasis.  However, these treatments may have already been tried or may no longer be effective.  Since liver failure is tantamount to death, prostate cancer growth in the liver needs to be stopped immediately, regardless of how the disease is faring in the bones or nodes.


Much that has been learned about the treatment of liver metastases comes from reviewing common methods for managing metastatic colon cancer. The liver is the cancer’s preferred site of metastatic spread for colon cancer.  Treatments that have been employed include surgery, radiation and blockage of the blood supply to the liver by embolization of the arteries, all with variable success.  More recently, radioactive microspheres injected directly into the tumor, called SIR-Spheres, have shown notable efficacy with very tolerable side effects.


Prostate cancer and colon cancer are similar in that they are both adenocarcinomas which means they are derived from glands. Therefore, they are likely to have similar susceptibility to radiation.  As such, we have been administering SIR-Spheres to a limited number of prostate cancer patients with liver metastases.  Results have been encouraging with a notable improvement of survival compared to our historical experience treatment patients with liver metastases without SIR-Spheres.  Our preliminary results using SIR-Spheres in six patients is being presented at the 2016 Genitourinary Cancers Symposium - San Francisco in January 2016.