In contrast to the lack of FDG uptake in benign PEComas, uptake of FDG occurred in malignant lesions in several cases. Subject 9 had a PET scan performed to evaluate a lung nodule, which ultimately proved to be a lung adenocarcinoma. As shown in Figure 4, the FDG-PET scan revealed increased uptake in the left upper lobe (LUL) tumor but not in other regions of the lung affected by LAM. Another patient with TSC-LAM and polycystic kidney disease (subject 7), who was 7 years status post bilateral nephrectomy and renal transplant, had a malignant uterine PEComa (Fig 5E to G) and multiple spiculated pulmonary nodules discovered during evaluation for lung transplantation. A genotype analysis performed of the patient's peripheral blood revealed a very large gene deletion involving all TSC2 exons. A FDG-PET scan performed after the hysterectomy showed uptake in some of her pulmonary masses, but no FDG uptake in her multiple abdominal lymph nodes, abdominal cystic lymphangioleiomyomas, or LAM-affected lung tissue (Fig 5, A–D). In this case, the FDG-PET scan revealed that the abdominal masses were most consistent with benign rather than malignant PEComas, a finding that had important prognostic implications for the patient. After modification of her renal immunosuppressive regimen to include sirolimus, there was significant reduction in the size of the patient's abdominal masses, and her pulmonary nodules remained stable in size and number over a 15-month follow-up period (not shown). Figure 6 displays a third case where FDG-PET scanning proved to be clinically useful in a patient with LAM. This individual (subject 11) had Hodgkin lymphoma (nodular sclerosing type), based on increased FDG uptake in the supraclavicular and mediastinal lymph nodes, and the biopsy findings for the supraclavicular lymph node. Initially, she was diagnosed and treated for stage IV Hodgkin disease, based on the presence of what were believed to be necrotic retroperitoneal lymph nodes on CT scan (Fig 6B). However, the abdominal masses were negative on staging FDG-PET scan, a chylous effusion developed, and a high-resolution CT scan of the chest revealed cystic changes that were typical for LAM. A percutaneous needle biopsy of the paraaortic retroperitoneal mass revealed a spindle cell neoplasm consistent with LAM, although HMB-45 staining was not demonstrated in the small sample obtained. Her abdominal lymphadenopathy, chylous effusion, and pulmonary cysts were attributed to LAM, and her staging was revised based on this information. Finally, a patient with biopsy-documented LAM (subject 12) was advised by her gynecologic consultant to have her enlarged retroperitoneal lymph nodes biopsied to rule out ovarian carcinoma or lymphoma (Fig 6C). The PET scan findings were negative except for focal uptake in the ovary (not shown), possibly consistent with ovulation, and the biopsy was deferred.