Benefit of PET and PET/CT in ovarian cancer remains unproven

Due to the lack of studies, there is currently no proof that patients with ovarian cancer can benefit from PET alone or in combination with CT. With regard to diagnostic accuracy, recurrences can be detected earlier and more accurately with PET or PET/CT than with conventional imaging techniques in certain cases. So concluded the final report by Germany's Institute for Quality and Efficiency in Health Care (IQWiG) in Cologne, which was published May 23.

Ovarian cancer is the fifth most common malignant tumor in women. Every year, 15.9 women in every 100,000 are diagnosed with the disease in Germany, and it claims the lives of eight in 100,000 women per year. Ovarian tumors normally have no symptoms for a long time; they are often only discovered at a late stage, according to IQWiG.

Many experts hoped that an investigation using PET or PET/CT alone or in combination with other methods would be better able to distinguish between benign and malignant tumors when ovarian cancer is suspected, according to report authors. The other hope was that it would help classify cancerous tumors into the correct stage, make it easier to assess whether they respond to treatment and show earlier and with greater certainty whether a recurrence or secondary tumor has occurred. This information would have informed better treatment recommendations.

IQWiG, therefore, said it searched the international literature for studies investigating the effects of diagnosis using PET or PET/CT on health aspects of direct relevance to patients. For example, the results of this research—and an appropriately tailored treatment—may contribute to patients having better chances of survival, spare them unnecessary operations or other diagnostic procedures or improve their quality of life.

However, the search for such studies was "unsuccessful," according to the authors, so the question of the patient-relevant benefit of PET or PET/CT was unanswered.

In addition, IQWiG said it searched for studies in which the diagnostic accuracy and prognostic power of PET or PET/CT were compared with other diagnostic methods. The basic question is how often a PET investigation gives a correct result. On the one hand, it should overlook true, cancerous tumors as rarely as possible, but on the other, it should not awake any false suspicions.

The results of a total of 40 individual studies on this topic were evaluated; however, these studies permit a robust conclusion only in respect of the detection (or exclusion) of a recurrence, where PET or PET/CT appears to be more reliable than other methods. Nevertheless, it remains "unclear" whether this only applies to patients in whom symptoms (e.g. pain) have already occurred, or also to those in whom routine screening has shown an abnormal blood test result, wrote the report authors. This is because only very few studies give precise details on this point.

Since even the above patients have not been investigated to determine whether the higher test accuracy of PET or PET/CT has positive effects on mortality, the burden of disease or the quality of life, IQWiG suggested that a patient-relevant benefit of PET or PET/CT is not proven. For instance, it is particularly questionable whether a recurrence detected by PET or PET/CT can actually be better treated—and the patient thereby has a noticeable advantage.

Thus, the German institute said it is essential that doctors fully inform their patients not only of the possible benefits in the form of an earlier diagnosis, but also of the possible harms. The latter can arise from an earlier start to second-line treatment associated with considerable side effects, but not with a prolongation of survival. Hence, they also recommended that studies are urgently needed to investigate the patient-relevant benefit of PET or PET/CT in the diagnosis of ovarian cancers in direct comparison with conventional diagnostic techniques.