Tc-99m labelled Cationic Lipophilic Complexes: An Update of their Emerging Roles in Oncology

Objectives 1. To present the role of ^99mTc-labeled cationic lipophilic complexes in the diagnostic investigation, prognostication, and follow-up of cancer patients. 2. To demonstrate specific applications of these radiotracers in oncology after the development of hybrid systems. 3. To evaluate the advantages and disadvantages of ^99mTc-labeled cationic lipophilic complexes imaging relative to positron emission tomography (PET) in oncology.

Methods ^99mTc-sestamibi and ^99mTc-tetrofosmin have a widely-established role in myocardial perfusion imaging. However, these radiolabeled cationic lipophilic complexes could also have important applications in oncology as tumour-seeking agents in the investigation of various human malignancies, including lung cancer, hematologic malignancies, breast cancer, thyroid cancer, and brain tumours. Single photon emission computed tomography (SPECT) represents a valuable diagnostic tool in a number of clinical conditions. Therefore, despite the eminent contribution of positron emission tomography (PET) in cancer imaging with fluorine-18-labeled fluorodeoxyglucose (¹⁸F-FDG), SPECT with either ^99mTc-sestamibi or ^99mTc-tetrofosmin may be of value in the diagnosis and staging of the primary tumour, the prediction of therapy response, the monitoring of treatment, and the detection of disease recurrence. Although these SPECT methods are characterised by high sensitivity in cancer patient management, their diagnostic accuracy is limited by the unfavourable structural delineation of the pathologic processes. Notably, the development of the hybrid systems, that combine the functional SPECT results with the anatomical information obtained through computed tomography (CT), may lead to a wider use of ^99mTc-sestamibi or ^99mTc-tetrofosmin in oncology. The integrated dual-modality imaging (SPECT/CT) might help both in the planning of radiation therapy and the detection of local recurrence during follow-up. Moreover, previous studies have demonstrated an association of ^99mTc-sestamibi and ^99mTc-tetrofosmin uptake with important factors in the failure of chemotherapy, such as tumour expression of P-glycoprotein (Pgp). Thus, SPECT could provide additional evidence regarding tumour response to chemotherapy. Finally, the widespread availability of SPECT cameras and the lower cost for performing SPECT studies in community-based facilities represent major advantages of SPECT over PET studies, which are also dependent on a limited number of experts for PET images interpretation in many countries.

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