The precise place for PetScan in the diagnostic setting is yet to be determined.
When a mass is profoundly situated within the body, it may be interesting to try to differentiate between a benign and a malignant tumour. This supplementary examination may be useful, but is not necessarily essential.
For instance, PetScan is quite useful for solitary lung nodules, pancreas tumours or a few mammary tumours.
However, this examination is not a histological study, which is necessary before any treatment. Because PetScan does not offer absolute specificity, a histological study is always mandatory. Intervention radiology techniques have been greatly developed allowing the necessary sampling for pathological studies.
They concern situations where a metastatic tumour has been proven without detection of a primitive tumour (in particular isolated metastatic nodes).
If efficient treatment is available (even if only palliative), it is useful for the patient to have knowledge of his/her primitive tumour, and PetScan may be of considerable help.
PetScan allows the detection of metastatic nodes, unsuspected by other imaging techniques. With the simultaneous use of a scanner, this research is even more accurate.
The therapeutic strategy can be therefore modified:
- Surgery indications are not proposed due to the presence of distance metastases : bronchial carcinoma, rectocolic cancer, pancreas cancer
- On the opposite, more intensive chemotherapies may be proposed : inflammatory breast cancer, lymphoma, testis cancer, ovarian cancer, sarcoma
However, two restrictions should moderate the current enthusiasm among many physicians:
- it might often be useful to confirm, by pathological study, the exact signification of a 'pathologic' image,
- It has not been proven that the local therapeutic abstention (or, inversely, intensification) related to the discovery of pathological isotopic images is genuinely useful for the patient (no randomised study has been carried out to date).
The same arguments apply for the diagnosis of distant metastases.
In the case of distant metastasis diagnosis, ,PetScan offers the same advantages (examination simplicity) and the same restrictions (image specificity).
Moreover, no randomised studies have been carried out to establish the value of abstention due to the discovery of occult metastases: for instance, would a simultaneous metastasectomy be useful? On the other hand, general treatment modalities are most often less active than local treatment for local masses, and should surgery always be denied to patients even for palliative purposes.?
Therefore, this very sensitive examination raises new strategical therapeutic questions which should lead to rigorous randomised studies.
PetScan allows the differentiation between relapsing tumour within a scar from necrotic tissue. This technique therefore corrects the imperfections of traditional imaging.
This new examination is of particular interest when clinical symptoms of relapse exist, when traditional imaging fails to prove this relapse and when local (or general) treatment may be useful for the patient (local relapse surgery, radiotherapy, efficient chemotherapy, hormonotherapy).
In the case of a solitary increase of a tumour marker, (more or less specific), in the absence of any clinical symptoms, no study has yet demonstrated that treatment increases patient benefit (except in the case of solitary metastasis surgery). The utility of PetScan in such situations is therefore dubious, and is possibly no greater than marker surveillance alone.
Randomised scientifically conducted studies are necessary to prove the usefulness of such surveillance in treated patients.