Those who are used to seeing the bone scans of men with advanced prostate cancer will have long realized that (usually) bone metastases seem to appear in a orderly manner over time: initially in the pelvis and lower spine, then up through the spine and out into the ribs and shoulders, and then out into the long bones of the arms and legs. Metastases to the bones of the skull tend to appear only very late in the disease progression.
There is therefore nothing particularly surprising about data from a recent study by two Chinese radiologists … except for their demonstration of the degree of accuracy and consistency with which this pattern of the spread of bone metastases appears to occur.
Wang and Shen conducted a detailed, retrospective analysis of the bone scans of 144 patients as a method of exploring the distribution features of metastatic prostate cancer lesions to bone. All the bone scans had been carried out using [99mTc]methylene diphosphonate as the nuclear imaging agent, and all the patients had been diagnosed with pathologically proven prostate cancer.
The authors were able to show the following:
- 2,000 metastatic prostate cancer lesions were detected in the bones of 102/144 patients.
- Of these 2,000 lesions
- 28.9 percent were distributed among the ribs.
- 14.8 percent were detected in thoracic vertebrae (the upper bones of the spine).
- 13.8 percent were detected in the ilium (the largest bone in the pelvis).
- 8.0 percent were found in the lumbar vertebrae (the lower bones of the spine).
- The distribution of metastatic lesions in the bones was directly correlated with the total number of lesions.
- In men with fewer bone metastases, metastatic lesions in the vertebrae and pelvis comprised up to 84.5 percent (49/58) of all bone metastases.
- As the total number of bone metastases in an individual patient increased, so did the probability that they would be found to extend beyond the vertebrae and the pelvis.
- 903/912 metastatic bone lesions (99.0 percent) that were not in the pelvis or the vertebrae coexisted with metastasis to the pelvis or the vertebrae.
- Only 9/912 metastatic bone lesions (1.0 percent) were found in men who had no metastasis to the pelvis or the vertebrae.
- 571/578 metastatic costal bone lesions (98.8 percent) — i.e., those in the ribs – coexisted with metastases to the vertebrae.
- Only 7/578 metastatic costal bone lesions (1.2 percent) were found in men who had no metastasis to the vertebrae.
- There was no difference between the numbers of metastases to bones on the right or left sides of the body.
The authors conclude, as one might expect, that metastatic prostate cancer lesions in the bones of men with advanced forms of prostate cancer are initially located mainly in the vertebrae and the pelvis. However, they are also able to conclude that metastatic lesions to the bones are characterized by spreading to the left and right sides of the body in a random manner and that there is a surprising degree of “orderliness” to the distribution of metastases across the whole body.
It is apparent that the occurrence of isolated bone metastasis (presumably because of metastasis to distant areas of bone from the pelvis) is a relatively rare event, and that in the vast majority of patients metastasis does indeed occur in a much more standardized manner … from prostate to pelvis and vertebrae and then out to more distant bones.
It will be interesting to see if the same or other authors are able to get insights into the distribution of visceral metastases in men with advanced prostate cancer based on CT and/or other imaging data, and whether this type of metastasis also occurs in such an orderly manner most of the time.