Efficacy of Tc99m-MDP and Tc99m-MIBI in detecting malignant tissue in the breast

Most breast cancer patients come in stage II and above, many times delayed due to absence of a definitive diagnostic procedure. X-ray mammography and other imaging modalities lack in specificity in comparison to scintimammography (SMG) which is performed using Sestamibi or Tetrofosmin. Efforts have been made to use MDP in place of Sestamibi which is significantly cheaper and has also the advantage of obtaining bone scan on the same day in one go. The purpose of this study is to compare the efficacy of both agents. 123 consecutive patients with confirmed diagnosis of breast cancer were subjected to scintimammography using 20 mCi of Tc99m-MDP (BRIT, BARC, Mumbai) and a dual headed gamma camera using standard technique. Scintimammography was performed in another 105 consecutive similar patients using the same standard technique and equipment but with Tc99m-Sestamibi (Sanlar). 30 patients clinically suspected of having breast cancer and later confirmed were subjected to SMG using both agents on two separate days. Each scan was evaluated by two nuclear physicians. Ratio of tracer uptake in the lesion and normal tissue was calculated. Sensitivity and specificity was found to be 96.9 % and 92.2 % respectively in patients performed with Tc99m-MDP and 98.1 % and 93.7 % respectively in patients using Tc99m-Sestamibi. Out of 30 cases in whom SMG was performed using both agents, 28 (93 %) showed concordant findings (both positive 16, both negative 12). In two patients Sestamibi scans were positive but MDP scans were negative. In 16 MIBI positive cases 3 showed concentration in axillary lymph nodes which was not seen in MDP scan. In 16 MDP positive cases 4 showed metastatic involvement of the skeletal system. The activity ratio in MIBI and MDP scans were similar and varied from 1.3 to 5.7. In one case a small lesion in the other breast was not visualized in MDP scan. The sensitivity and specificity found in our studies is higher than in many published multicentric studies which may be due to the fact that most patients were in stage II and higher at the time of diagnosis. Tc99m-Sestamibi is potentially better than Tc99m-MDP in detection of malignant lesions. However, MDP is not only cheaper, but the whole body bone scan which can be performed in one go can provide vital information regarding metastatic involvement of the skeletal system. Tc99m Sestamibi remains the choice radiopharmaceutical for early diagnosis of breast cancer. However, Tc99m-MDP can be recommended for diagnosis of breast cancer in cases suspected to be in stage II and higher with the additional benefit of getting vital information regarding involvement of skeletal system. (author)