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Photoacoustic monitoring of circulating tumor cells released during medical procedures

Many cancer deaths are related to metastasis to distant organs due to dissemination of circulating tumor cells (CTCs) shed from the primary tumor. For many years, oncologists believed some medical procedures may provoke metastasis; however, no direct evidence has been reported. We have developed a new, noninvasive technology called in vivo photoacoustic (PA) flow cytometry (PAFC), which provides ultrasensitive detection of CTCs. When CTCs with strongly light-absorbing intrinsic melanin pass through a laser beam aimed at a peripheral blood vessel, laser-induced acoustic waves from CTCs were detected using an ultrasound transducer. We focused on melanoma as it is one of the most metastatically aggressive malignancies. The goal of this research was to determine whether melanoma manipulation, like compression, incisional biopsy, or tumor excision, could enhance penetration of cancer cells from the primary tumor into the circulatory system. The ears of nude mice were inoculated with melanoma cells. Blood vessels were monitored for the presence of CTCs using in vivo PAFC. We discovered some medical procedures, like compression of the tumor, biopsy, and surgery may either initiate CTC release in the blood which previously contained no CTCs, or dramatically increased (10-30–fold) CTC counts above the initial level. Our results warn oncologists to use caution during physical examination, and surgery. A preventive anti-CTC therapy during or immediately after surgery, by intravenous drug administration could serve as an option to treat the resulting release of CTCs.