IS PET BEST BET TO SPOT TUMOUR SPREAD?
"Is positron emission tomography (PET) scanning the best way to look for the spread of breast cancer or lymphoma?" inquires B. TOEWS, MD, of Coquitlam, BC.
At this point in time, the answer is a definitive "likely no." I believe we're right on the cusp of a new age of tumour scanning with a big role for PET, but there are still many restrictions and doubts right now. For various reasons -- not the least of which is severely limited access to state-of-the-art PET scanning technology in Canada -- the imaging modalities of choice are still CT for assessing visceral and nodal tumour spread, and bone scintigraphy for skeletal system staging and monitoring bone responses to therapy. PET can monitor pathophysiologic changes over time, unlike purely anatomic imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI). As further results from prospective trials emerge, PET scanning is gaining momentum as a viable complementary tumour imaging modality, if not a primary diagnostic tool. It looks like PET may be more accurate for detecting nodal lymphoma than CT, and it's more sensitive and specific than bone scintigraphy, with a high positive predictive value, to assess bone involvement in malignant lymphoma. But compared to CT, MRI, tissue biopsy and clinical follow-up, PET isn't sensitive enough to be used as an independent imaging method in patients with suspected lymphoma, especially for small abdominal lesions. It's accurate for assessing residual disease, however, and for following patient response to therapy. For managing breast cancer, PET is the only noninvasive imaging procedure that will detect it in the breast, lymph nodes, lung, liver, bone and bone marrow with a high sensitivity, specificity, and accuracy. Although the full impact of PET on tumour diagnosis and management has yet to be determined, the future implications include: primary detection and differentiation of malignant tumours, staging local nodal disease, detecting residual disease and distant metastatic spread, monitoring tumour response to therapy. If you have access to PET scanning facilities in your region, call your local radiology group and discuss the present and potential applications of PET in tumour management available to you. MM (References: Semin Nucl Med 1999 29(1):49-56; Br J Radiol 1999 72(863):1064-1068; Radiol 1997 203(3):795-800; J Nucl Med 1999 40(9):1407-1413; Clin Nucl Med 2000 25(10):789-795; Radiology: Diagnosis-Imaging-Intervention (Taveras & Ferrucci, eds.) 2001 Vol. 5:ch. 27A.)