癌症是人类生命的一大威胁，而肿瘤的侵袭和转移是癌症患者死亡的主要原因之一。在这一复杂过程中，循环肿瘤细胞（CTC）等血液循环中的粒子起到十分关键的作用，所以监测血液循环中的CTC和其他肿瘤相关的粒子可以促进肿瘤转移的研究。光学活体流式细胞仪（IVFC）是一种基于激光的新兴技术，可在体内无创监测循环细胞，包括CTC等肿瘤相关的颗粒。这一强大的工具已被广泛应用于癌症相关的多个领域，尤其是肿瘤转移研究。因此，总结分析IVFC在肿瘤转移研究中的应用具有重要意义。本文介绍IVFC的检测原理，总结基于荧光发光、光声效应、计算机视觉等光学技术的荧光活体流式细胞仪、光声活体流式细胞仪、图像活体流式细胞仪等IVFC分类，对IVFC应用于肝癌、前列腺癌、乳腺癌、黑色素瘤等肿瘤转移的相关研究进行综述，并总结和展望IVFC对肿瘤转移研究的应用。

液体活检是近些年新兴的体外诊断技术, 通过从肿瘤患者外周血中筛选出肿瘤细胞来检测和分析其上携带的各种生命信息, 具有便捷、侵入性小、检测精度高等特点。循环肿瘤细胞(Circulating Tumor Cells, CTCs)作为液体活检的重要标志物之一, 对于癌症的早期检测、疗效评估以及预后监测具有重要意义。但是血液中CTCs的含量非常少, 通常每毫升血液中仅含有1~10个CTCs, 还有数以百亿计的血细胞, 所以CTCs的富集以及筛选是液体活检中的难题, 对CTCs所携带的生命信息进行解析是关键。总结了经典的CTCs分离方法并重点概括了CTCs的检测技术。

The fluorescence-based in vivo flow cytometry (IVFC) is an emerging tool to monitor circulating cells in vivo. As a noninvasive and real-time diagnostic technology, the fluorescence-based IVFC allows long-term monitoring of circulating cells without changing their native biological environment. It has been applied for various biological applications (e.g., monitoring circulating tumor cells). In this work, we will review our recent works on fluorescence-based IVFC. The operation principle and typical biological applications will be introduced. In addition, the recent advances in IVFC flow cytometry based on photoacoustic effects and other label-free detection methods such as imaging-based methods, diffuse-light methods, hybrid multimodality methods and multispectral methods are also summarized.

Metastasis is a very complicated multi-step process and accounts for the low survival rate of the cancerous patients. To metastasize, the malignant cells must detach from the primary tumor and migrate to secondary sites in the body through either blood or lymph circulation. Macrophages appear to be directly involved in tumor progression and metastasis. However, the role of macrophages in affecting cancer metastasis has not been fully elucidated. Here, we have utilized an emerging technique, namely in vivo flow cytometry (IVFC) to study the depletion kinetics of circulating prostate cancer cells in mice and determine how depletion of macrophages by the liposome-encapsulated clodronate affects the depletion kinetics. Our results show different depletion kinetics of PC-3 cells between the macrophage-deficient group and the control group. The number of circulating tumor cells (CTCs) in the macrophage-deficient group decreases in a slower manner compared to the control mice group. The differences in depletion kinetics indicate that the absence of macrophages facilitates the stay of prostate cancer cells in circulation. In addition, our imaging data suggest that macrophages might be able to arrest, phagocytose and digest PC-3 cells. Therefore, phagocytosis may mainly contribute to the depletion kinetic differences. The developed methods elaborated here would be useful to study the relationship between macrophages and tumor metastasis in small animal cancer models.

Cancer (malignant tumor) is one of the serious threats to human life, causing 13% of all human deaths. A crucial step in the metastasis cascade of cancer is hematogenous spreading of tumor cells from a primary tumor. Thus, isolation and identification of cells that have detached from the primary tumor and circulating in the bloodstream (circulating tumor cells, CTCs) is considered to be a potential alternation to detect, characterize, and monitor cancer. Current methods for isolating CTCs are limited to complex analytic approaches that generate very low yield and purity. Here, we propose a high throughput 3D structured microfluidic chip integrated with surface plasmon resonance (SPR) sensor to isolate and identify CTCs from peripheral whole blood sample. The microfluidic velocity-field within the channel of the chip is mediated by an array of microposts protruding from upper surface of the channel. The height of microposts is shorter than that of the channel, forming a gap between the microposts and the lower surface of the channel. The lower surface of the channel also acts as the SPR sensor which can be used to identify isolated CTCs. Microfluidic velocity-field under different parameters of the arrayed microposts is studied through numerical simulation based on finite element method. Measurement on one of such fabricated microchips is conducted by our established optical Doppler tomography technique benefiting from its noninvasive, noncontact, and high-resolution spatialresolved capabilities. Both simulation and measurement of the microfluidic velocity-field within the structured channel demonstrates that it is feasible to introduce fluidic mixing and causes perpendicular flow component to the lower surface of the channel by the 3D structured microposts. Such mixing and approaching capabilities are especially desirable for isolation and identification of CTCs at the coated SPR sensor.