In November, we’re talking about imaging prostate cancer.
Dr. Snuffy Myers frames this month’s discussion for us.
“Our ability to image prostate cancer metastases has improved dramatically over the past few years. CT and bone scans, which have been the standards for decades, typically image a cancer mass larger than 1 cm (0.4 inches). Newer imaging techniques have lower limits that approach 1-4 mm. Dramatic changes like these have a way of disrupting the status quo.
The current guidelines for the treatment of metastatic prostate cancer are based on clinical trials where metastases were detected with CT or bone scans. Do these treatment guidelines still hold for metastases too small to be found by CT or bone scan, but detectable with the newer, more sensitive imaging techniques? There are reasons to suspect we might begin to detect prostate cancer at a different stage in its evolution.
The concept of cancer dormancy is commonly used to explain a long interval between initial treatment with surgery or radiation and subsequent appearance of metastatic disease. For both breast and prostate cancers, more than 10 years can pass between treatment with curative intent and the appearance of detectable metastatic disease.
Several mechanisms have been identified that can lead to cancer dormancy. Two of these mechanisms might result in cancer masses potentially detectable by the newer imaging techniques. First, cancer dormancy can result when the cancer mass fails to attract a blood supply and thus is starved of both oxygen and food. The second is that cancer dormancy can result from ongoing immune attack on the cancer. Both mechanisms can allow cancer masses above 1 mm that overlap with the lower limit of the newer scans.
Cancer dormancy is associated with greater resistance to cytotoxic chemotherapy and hormonal therapy. The implication is that we may increasingly detect prostate cancer metastases that pose no immediate threat to the patient because they are dormant. Additionally, these metastases may respond poorly to standard treatment options. All of these factors would argue for caution in making treatment decisions based on the newer generation of scans.