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Diagnosis by PET of Refractory Breast Cancer without any Damage to the Body
--- Towards Realization of Theranostics, the Diagnosis and Treatment Method Using the Same Drug ---

Breast cancer ranks first in female cancer incidence rate by site. In particular, "HER2-positive breast cancer" has high metastatic and relapse rate, and is difficult to treat. It accounts for 20 to 30% of the total breast cancer. HER2-positive breast cancer has HER2 protein on its surface of cancer cell. "Trastuzumab", an anti-cancer drug, which zeroes in on and destroys the cancer, has recently been developed. Breast cancer treatment has accordingly changed a great deal. Trastuzumab is said to suppress the growth of breast cancer cells by binding to the protein and have a great therapeutic effect.
The PET exam is used to early detect cancers. This is a method to detect cancers by means of the property that the cancer cells are likely to consume a lot of sugar. First, a sugar-like compound is injected to the patient, after being labeled by radioisotope (transformed into PET probe). Then the PET probe moves around the body and is taken in the cells with sugar metabolism activated. This helps us visualize high-grade tumors for diagnosis. However, we had to pinprick the diseased site to take cells (needle biopsy), since the PET exam cannot tell which the cancer cells are HER2-positive or -negative.
Researchers of RIKEN Center for Molecular Imaging Science have developed a technique for diagnostic imaging of HER2-positive cancer cells using Trastuzumab for PET probe. The drug was labeled by radio isotope of copper (⁶⁴Cu) with low level radiation exposure. We could safely trace the movements of Trastuzumab, since the patients were exposed to the same level of radioactivity as they undergo a traditional PET exam. The result of 14 case clinical tests for the patients undergoing treatments using the drug was that metastases to primary lesions, bones and brains as well as shrinkage of tumors by treatments were recognized.
Utilization of the very therapeutic agent as a diagnostic one suggests the possibility of realization of "Theranostics", where a series of medical procedures such as diagnosis, treatment and prognostic observation will be integrated. In the future, we are going to enhance the certainty of diagnostic imaging, apply it to other types of cancers, and furthermore work toward practical use of it.

Concentration of Trastuzumab PET Probe in Metastatic Foci of HER2-Positive Breast Cancer