Is PSMA PET-CT Better than Bone Scan? When and Why

Abstract

Prostate cancer (PCa) has a unique tropism to bone. Indeed, bone is the most frequent site of distant metastasis and cause of morbidity due to skeletal complications. 99mTc-Methylene diphosphonate (MDP) bone scintigraphy/ scan (BS) is the current standard imaging due to increase adsorption of the tracer at osteoblastic sites. However, it has limited specificity due to false positives in degenerative changes, benign causes and false negatives in bone marrow metastasis and lytic lesions. Another drawback of BS is flare response. Prostate Specific Membrane Antigen (PSMA) has been the most studies target in prostate cancer imaging in recent time due to 100-1000 time overexpression in cancer cells. 68Ga-PSMA-11, a small molecule with PSMA enzyme inhibition activity has been found promising in recurrence and lymph-node staging. In our experience of 97 staging prostate cancer patients, PSMA PET-CT showed 57.41% with pure sclerotic metastasis. Mixed (33.33%), marrow (7.14%) and lytic (2.3%) types of lesions constitute the rest and thus BS alone in these patients may leads to underestimation of bony disease burden. PSMA has not been found positive in degenerative changes however its role in response to anti-androgen needs caution due to know synergistic effect on PSMA expression. We concluded, PSMA PET-CT would have better sensitivity and specificity due to unique distinction for detecting non-sclerotic metastases. We presumed if PSMA has been performed for staging workup then there is limited role of BS except in clinical trial patient. Overall PSMA PET may become one-stop-shop for PCa workup.