K

Anterior

Left lateral

Figure 5. Scintimammogram with 99mTc-sestamibi in a patient with a primary breast cancer in the left breast (arrow) measuring 2 cm. Note normal thyroid activity (arrowheads) on the anterior view; the heart and liver activity is saturated out. A small amount of activity is seen in the nipple ultrasound and MRI. Even if these additional studies show probable cancer, biopsy confirms the diagnosis in only about 30% of patients. Therefore, while mammography has a high negative predictive value, it has low specificity, even in conjunction with additional conventional imaging. The specificity of mammography, ultrasound and MRI is particularly poor in patients with dense breasts, previous breast conserving surgery and implants.

It has been postulated that scintimammography with 99mTc-sestamibi has a role in the management of this latter population of patients (Fig. 5). In several large series, high sensitivity (80-92%) and high specificity (80-100%) have been demonstrated; negative predictive values of up to 96% have been reported. However, these data are for lesions >1 cm in diameter and diagnostic accuracy is lower for smaller

Scintimammography is not a screening tool, but as a supplementary examination to mammography and ultrasound it may have a role in evaluating specific populations of patients as defined above and in evaluating inconclusive morphological images. The technique is likely to become routine for the evaluation of the dense breast and the assessment of recurrence in patients who have had previous surgery. The advantages of functional imaging become clear in these settings.

Gastrointestinal Tract

CT and ultrasound are the primary investigations for staging and assessing recurrence of these tumors. Nuclear medicine techniques may contribute to management of some cases of esophageal and colorectal cancers.

lesions.

Figure 6. Coronal PET images of a patient with a large metastatic colorectal lesion in the left lung (arrow) and a local recurrence in the pelvis (arrowhead). (Courtesy of ADAC Labs and Dr. J.-F. Gaillard, HIA Val de Grace, Paris, France.)

Esophageal Cancer

The incidence of esophageal cancer in the United States is 3.5/100,000, although it is considerably higher in parts of China and is more common in France, Singapore, Iceland and Switzerland. Initial presenting symptoms include dysphagia and weight loss. Two year survival is only 20%.

Early data have suggested that FDG imaging may be an important tool in staging this population of patients. FDG images were more accurate than CT in demonstrating spread to mediastinal lymph nodes and were considered to have altered staging and management in approximately one-third of the patients. As surgical and radiotherapeutic morbidity are high, accurate staging of these patients will not only improve management but should also contribute to improved quality of life.

Colorectal Cancer

Colorectal cancer affects approximately 1 in 20 people in the United States and in most developed countries. If diagnosed early, it is curable by surgery. Spread is initially through the muscularis mucosa and into the submucosa. With penetration of the bowel wall, it spreads by local invasion; nodal metastases occur in approximately 20% of patients in whom the cancer is localized to the bowel wall. Nodal spread is usually through the lymphatic network along the major vessels. The liver is the commonest site of distant metastasis. Treatment of advanced disease is by chemotherapy with surgery only if required for control of symptoms.

FDG has no role in the initial staging of this population. However, in patients with locally advanced disease, FDG has been shown to be an effective management tool for identifying distant metastases (Fig. 6). The most important role of FDG imaging is in discriminating between residual tumor and scar in patients with prior therapy and in identifying the presence of local recurrence (Fig. 7). For both indications FDG has demonstrated sensitivities of the order of 90-95% compared

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