PET/CT Found Effective in Detection of Breast Cancer Metastases

The new findings may mean less stress and more timely therapy for patients, and could make the longtime use of radionuclide bone scans for breast cancer obsolete in this setting.

Approximately one-third of women diagnosed with early-stage breast cancer will have their cancer metastasize to other parts of the body, with the bone being the most common site of initial detectable spread. Controversy continues as to whether CT and bone scans should be standard in evaluating patients for these metastases, or whether integrated PET/CT scanning might be more effective at detecting breast tumors that have reached neighboring bones. Of the about 200,000 cases of early stage breast cancer diagnosed in the United States each year, one in three will eventually metastasize to other areas of the body. In nearly half of these women, the first detectable distant site is the bone. (Distant sites can include any location in the body other than the lymph nodes located closest to the primary tumor.) Yet there is no standard approach for the detection of such metastases.

Bone scans, PET, and CT all continue to be used alone or in combination for the detection of breast cancers suspected to have spread. In some cases, physicians use all three imaging techniques. Each has its own strengths. For example, bone scans detect bony regions in the process of growth or repair, which can be a sign of metastatic disease. PET, on the other hand, evaluates abnormalities of biochemical activity in the body, such as cells that metabolize glucose unusually fast. Such features are a hallmark of a cancer cell. Meanwhile, CT generates anatomic images that can help physicians isolate and analyze the size and shape of tumors.

With one machine, simultaneous PET/CT draws on the strengths of each tool to both detect and locate abnormal and potentially cancerous cells. Moreover, its diagnostic reach can go beyond the bone. "In contrast with bone scans, which are only able to detect bone metastases, PET/CT has the advantage of concurrently imaging other common sites of breast cancer metastases such as the liver and lungs,” said lead author Patrick Morris, a breast cancer specialist at Memorial Sloan-Kettering Cancer Center (New York, NY, USA). "Therefore, PET/CT may not only be superior to bone scan for the detection of bone metastases, it may also be more convenient for patients.”

To find out whether PET/CT can be strong enough to abandon the need for additional testing and bone scans are simply redundant, the collaborative team identified 163 women with suspected metastatic breast cancer who had been evaluated by both PET/CT and bone scans at Memorial Sloan-Kettering between January 2003 and June 2008. As reported in the study, published in the June 2010 issue of the Journal of Clinical Oncology, the investigators compared the images and, when possible, correlated them with confirmatory biopsy results.

The majority of the dual tests were in agreement, leaving just 31 cases (19%) conflicting. In only two of these cases did a bone scan reach a positive result when the PET/CT did not, and neither woman received a subsequent confirmation of metastases. Of the remaining mismatched pairs, a majority represented cases of a PET/CT catching tumors that a bone scan missed. Dr. Morris estimates that some metastases could have been found by up to three or four months earlier using PET/CT instead of a bone scan. Furthermore, PET/CT uncovered cancer's spread outside the bone in 62% of patients in the study, which was led by senior author Dr. Heather McArthur, a breast cancer oncologist at Memorial Sloan-Kettering.

This improved accuracy and efficiency over older imaging applications may help patients and their clinicians save time and money, as well as emotional and physical pain. "False-positive radiology findings without a biopsy confirmation can lead to inappropriate therapeutic interventions and significant distress for the patient,” Dr. Morris noted. "False- negative findings, on the other hand, may result in delayed therapy, symptoms, and altered quality of life. Therefore, the development of a simple, reliable, and convenient test for imaging patients with suspected metastatic breast cancer is desirable.”

Dr. Morris added that the findings should be interpreted with caution, and that a long-term study with a more generalizable patient population would help validate the best method of metastases detection. "If this data holds true in a prospective trial, the issue can be laid to rest and PET/CT could replace CT plus bone scan,” noted Maxine Jochelson, director of radiology for the Breast and Imaging Center and a coauthor on the paper.

The interdepartmental research team, which also included Steve Larson, chief of the Nuclear Medicine Service at Memorial Sloan-Kettering, and Dr. McArthur, is currently working on the design of just such a trial. "We encourage patients to consider participating in these and future trials to examine the optimum imaging approach,” concluded Dr. Morris.

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Memorial Sloan-Kettering Cancer Center