October 10, 2008
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Bone scan vs. PET/CT in the assessment of skeletal metastatic disease progression

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A 68-year-old woman initially presented with intermittent abdominal pain and persisting left hip pain. She gave a history of early breast cancer and completed five years of tamoxifen one year ago. Her pertinent positive physical exam finding was decreased range of motion of the left hip. A CT chest/abdomen/pelvis showed an anterior mediastinal mass, multiple liver lesions, lytic and blastic lesion of the left 12th rib and multiple lytic lesions of the thoracic and sacral vertebrae. On bone scan, there was uptake in the left 12th rib and left sacroiliac joint (figure 1). A mammogram was negative. A biopsy of the liver lesion revealed an adenocarcinoma, ER-positive, PR-negative and HER2-neu negative. The patient was started on letrozole and zoledronic acid. Eight months later, the CT of the chest/abdomen/pelvis showed progression with increasing size of the mediastinal mass and number of liver metastases. Bone scan showed an interval response. She was started on fulvestrant (Faslodex, AstraZeneca) and noted to have stable disease three months later by tumor markers and PET/CT. Her skeletal system findings on PET/CT were hypermetabolic left 12th rib lesion with a standardized uptake value of 3.6 and hypermetabolic lytic sacral lesion with a standard uptake value of 4.1 (figures 2 and 3, top rows). Five months later, she experienced left forearm pain and there were increasing tumor markers. An X-ray of the forearm was negative and a bone scan showed stable disease in the left 12th rib and left sacrum with no evidence of metastatic disease in the left upper extremity (figure 1). Her skeletal system findings on PET/CT were left 12th rib lesion with a standard uptake value of 6.9 and lytic sacral lesion with a standard uptake value of 8.3 (figure 2 and 3, bottom rows), consistent with progression. Concordant with progression of skeletal metastatic disease, there was progression of mediastinal lymphadenopathy on both PET and CT (figure 4).

Figure 1: Initial and follow-up posterior planar views
Figure 1: Initial and follow-up posterior planar views from a whole body Technetium-99m MDP bone scan. Increased uptake in the left sacrum and left 12th rib is compatible with metastatic disease. Increased uptake in the left ankle correlates with history of known old injury. On the follow-up bone scan, no significant difference is detected.


Figure 2: Comparison of initial and follow-up PET/CT
Figure 2: Comparison of initial and follow up PET/CT examination demonstrates hypermetabolic activity (arrow) associated with lytic sacral lesion with interval progression as manifested by significant increase in standardized uptake values. Left image is axial CT scan, middle image is corresponding PET image, and the right image is fusion of PET and CT images displayed on color vs gray scale.

Figure 3: Comparison of initial and follow-up PET/CT
Figure 3: Comparison of initial and follow up PET/CT examination demonstrates hypermetabolic activity (arrow) associated with posterior left 12th rib lesion with interval progression as manifested significant increase in standardized uptake values. Image display format is same as figure 2.


Figure 4: Comparison of initial and follow-up PET/CT
Figure 4: Comparison of initial and follow up PET/CT examination demonstrates hypermetabolic activity (arrow) associated with increasing size of mediastinal lymph nodes. The findings are concordant with skeletal metastatic disease progression as evident in figures 2 and 3. Image display format is same as figure 2.

Source: M Ghesani

Vamsee Torri, MD, is a Fellow in Hematology/Oncology at St. Luke’s-Roosevelt Hospital Center.

Iwao Tanaka, MD, is a Resident in Radiology at St Luke’s-Roosevelt Hospital Center.

Munir Ghesani, MD, is an Associate Clinical Professor of Radiology at Columbia University College of Physicians and Surgeons and Attending Radiologist at St. Luke’s-Roosevelt Hospital Center.

DISCUSSION

F-18 FDG PET/CT and bone scans are utilized in the detection of suspected skeletal metastatic disease and in assessment of treatment response in patients with known skeletal metastatic disease. In general, osteoblastic lesions are more readily detectable by bone scan and osteolytic lesions from glucose-avid primary malignancies are more readily detectable by FDG PET/CT. Overall, PET/CT is shown to be more specific for metastatic disease than bone scan. Ohta and colleagues compared PET and bone scan in evaluation of skeletal metastases in 51 patients with breast cancer and found that the sensitivity, specificity and accuracy of the bone scan were 77.7%, 80.9% and 80.3%, respectively. Corresponding values of PET for the detection of bone metastases were 77.7%, 97.6% and 94.1%, respectively. The difference in specificity was statistically significant, with the P value of 0.0392. A meta-analysis of PET and bone scintigraphy was inconclusive as to whether FDG-PET or bone scintigraphy is superior in detecting osseous metastasis from breast cancer. However, FDG-PET had a higher specificity and can be used to monitor response to therapy. In a retrospective analysis of PET/CT in bone metastases from breast cancer, decrease in standard uptake values is shown to be an independent predictor for duration of response. The above case illustrates higher accuracy of PET/CT in assessing progression of bone metastases from breast cancer.

For more information:

  • Ohta M, Tokuda Y, Suzuki Y, et al. Whole body PET for the evaluation of bony metastases in patients with breast cancer: comparison with 99Tcm-MDP bone scintigraphy. Nucl Med Commun. 2001;22:875-879.
  • Shie P, Cardarelli R, Brandon D, et al. Meta-analysis: comparison of F-18 Fluorodeoxyglucose-positron emission tomography and bone scintigraphy in the detection of bone metastases in patients with breast cancer. Clin Nucl Med. 2008;33:97-101.
  • Tateishi U, Gamez C, Dawood S, et al. Bone metastases in patients with metastatic breast cancer: morphologic and metabolic monitoring of response to systemic therapy with integrated PET/CT. Radiology. 2008;247:189-196.