Abstract

Shahid Mahmood
Nuclear Medicine & PET Centre, Mount Elizabeth Hospital, Singapore

Breast cancer is one of the oldest known forms of cancer, with approximately 1.2 million new cases being diagnosed this year. It is the second leading cause of cancer deaths in women today (after lung cancer). Despite recognition of many risk factors, the primary cause still remains unknown in majority of the cases. Like other types of cancer, breast cancer is also considered to be a result of DNA damage, due to an increased rate of mutation (exposure to estrogens) and decreased repair (BRCA1, BRCA2 and p53 genes). It has also been found that combination of a newly discovered gene called BARD1 with BRCA2 gene may increase the risk of breast cancer to as much as 80 %.

Since, early detection and systemic therapy appears to provide significant survival benefit, accurate diagnostic assessment and identification of metastatic disease are essential. It is necessary to rule out sites of metastatic disease not amenable to local therapy, so that optimal treatment decisions can be made. Recent developments in proteomics and genomics have created an exciting era of Molecular Imaging, with expected benefits in oncology. The introduction of hybrid imaging by integrating two different modalities into a single system, like radionuclide imaging (PET and SPECT) with CT appears to be promising platforms.

F-18 FDG PET.CT potentially assists in identification of primary tumour, staging, analyzing appropriate treatment, and delivering targeted therapy to precisely destroy target cells, and assessing treatment effectiveness. PET.CT is very useful adjunct to mammography for diagnosis, particularly in patients with breast implants and dense breasts with approximately 94% accuracy. PET appears to be excellent for staging of palpable axillary lymph nodes, but in cases of non-palpable nodes, Axillary Lymph Node Dissection (ALND) is superior. However, F-18 FDG PET.CT is more sensitive than alternatives and perhaps more specific, for distant metastasis and recurrence.

Gene therapies, using viral and non-viral vectors have shown significant potential in treating breast cancer. Among these, virally delivered herpes simplex virus thymidine kinase (HSV-tk) gene appears to be promising, by providing a target for the development of reporter probes for imaging techniques. PECT.CT can successfully image HSV-tk gene expression, with new Fluorine-18 labeled PET reporter probes.

SPECT.CT is excellent for sentinel node lymphoscintigraphy and detection of equivocal bone metastasis. SPECT.CT is also helpful in planning and providing specific therapies for liver and soft tissue metastasis, diagnosed on PET imaging.

Hybrid imaging appears to be ultimate imaging devices for the future, helping to accelerate the adoption of molecular imaging. The early detection with advanced imaging methodologies and newer improved targeted therapies with fewer side effects may help to decrease the overall mortality, whereas advances in proteomics and genomics would be able to screen and identify high risk patients, reducing the incidence of breast cancer.