In summary, this study shows that :-
- There is a significant difference in serum PSA values between patients found to be bone scan negative for skeletal metastases and those found to be bone scan positive for skeletal metastases
- The negative predictive value of serum PSA at a cut-off point of 20ng/ml is 98.9%
- There is a significant difference in Gleason score between patients found to be bone scan negative for skeletal metastases and those found to be bone scan positive for skeletal metastases.
The relationship between serum PSA and radionuclide bone scan findings
Traditionally the radionuclide bone scan has been requested as a routine part of staging evaluations for newly diagnosed prostate cancer patients and during the follow-up of these patients post-treatment. The results of this study confirms those of previous research 3-6, which had demonstrated a close relationship between serum PSA levels and the risk of radionuclide bone scan being positive for skeletal metastases, suggesting that radionuclide bone scans on those patients with a low serum PSA level may be of little diagnostic value.
In this study, one patient was found to have skeletal metastases despite having a serum PSA of below 10ng/ml. It has been reported that patients with poorly differentiated tumours may have skeletal metastases and a low serum PSA. However, this was not the case with this particular patient who had a Gleason score of 4 which represents a well to moderately differentiated tumour. It is a possibility that in this case, the patient may have commenced hormone treatment prior to serum PSA measurement and this was not recorded in the case notes. However, this highlights the problem associated with planning to omit routine bone scan on patients believed to be in a low-risk group for developing skeletal metastases.
Therefore, it is important to identify patients with serum PSA levels which are inconsistent with the clinical stage and tumour burden, this includes those who have poorly differentiated tumours or those who have commenced hormone treatment.
The relationship between Gleason score, serum PSA and radionuclide bone scan findings
This study revealed significant differences in the mean Gleason score betwen those patients with skeletal metastases and those without skeletal metastases on bone scan. This study also confirms previous reports 7 that patients with a Gleason score above 4 are associated with rapid disease progression and increased metastatic spread potential. All the patients in this study with skeletal mestastases on bone scan presented with a Gleason score of above 4.
On the basis of this study, both null hypothesis stated in the Purpose section can be rejected.
Independently, both serum PSA levels and Gleason score can predict the likelihood of skeletal metastases, however the combination of Gleason score and serum PSA levels improves the prediction of the likelihood of a bone scan revealing skeletal metastases.
A radionuclide bone scan is not a necessary part of initial staging of prostate cancer patients or during follow up, unless one or more of the following criteria are met :-
- Serum PSA level > 20ng/ml
- Poorly differentiated tumour with Gleason score 7 - 10
- Symptoms suggestive of metastatic disease (ie unexplained bone pain)
- Commencement of hormone treatment