The Acousys Biodevices CTCS represents an entirely new type of flow cytometry tool. By using proven photoacoustic sensing methods, the CTCS system is capable of detecting single circulating tumor cells (CTC) such as melanoma in blood samples that would not otherwise be possible with conventional methods. Using fast laser pulses, tumor cells are illuminated in a photoacoustic flow chamber where if they absorb a fraction of the laser light produce an acoustic response for detection. Any tumor cells that can absorb the excitation wavelength naturally through pigmentation, (e.g. melanoma), through tagging are candidates for detection, making the CTCS a tool with broad clinical applications.