Monday, June 2, 2014

Further Hindrance in CTC measurement

     My partner’s previous post illustrated several issues which might change the number of detected CTCs in the bloodstream. While the study of CTCs holds many possibilities, my partner made a fair point to discuss that they have a fair number of limitations. One such limitation that he described was entrapment, in which CTCs sometimes get clogged within the capillaries, causing them to be underrepresented in blood samples. In my research I also stumbled upon similar phenomena in which the rate of CTC flow seemed to fluctuate. One particular study looked into the rate of CTC flow in both large and small blood vessels for both melanoma and breast cancer. The figures below display the results for these tests.

Figure 1. CTC Rate in Large Blood Vessels. CTCs were continuously monitored by PAFC in 150-250 μm diameter blood vessels of mice with the primary melanoma tumor in the flank. Graph a represents a 20 minute observation of the CTC rate at week 1 after inoculation. Graph b represents a 20 minute observation at week 2 after inoculation. The yellow squares highlight periods of CTC absence in the detection area.
     In this test, a set of mice was inoculated with melanoma cells in the flank in order to quickly develop metastatic skin melanoma. The CTCs were then periodically monitored by PA flow cytometry (PAFC) for 20 minutes in large blood vessels in the skin (150-250 μm in diameter). The figure above displays a rather curious outcome. The rate of CTCs appears to fluctuate wildly. In the observations after the first week, the CTC rate rose to their maximum at 6 CTCs per minute within 6 minutes and then quickly fell to 1 CTC per minute and remained at that level until the end of the 20 minute mark. Furthermore, there were several gaps in which the blood flow was CTC free for 1 to 3 minutes at a time. The rate also fluctuated at week 2 after inoculation. After 8 minutes, the CTC rate rose to its maximum level at 9 CTCs per minute, but then gradually decreased over the 20 minutes. Furthermore, while not as pronounced as the first week, there were also 3 CTC free gaps observed in the second week. Each of them was only 1 minute long.

Figure 2. CTC Rate in Small Blood Vessels. CTCs were continuously monitored with FFC in ear blood vessels for mice with breast cancer. Graph the CTC rates at week 2 after inoculation. Graph b represents the CTC rates at week 5 after inoculation. The grey squares highlight periods of CTC absence in the detection area.
     The figure above displays the tests done on mice inoculated with breast cancer. In these tests, CTCs were continually monitored with fluorescence flow cytometry (FFC) in the small blood vessels of the ear. At week 2 the CTC rate would quickly rise and fall. Within 15 minutes, the CTC rate gradually approached its maximum value of 4 CTCs per 5 minutes. However, this was immediately followed by a 20 minute CTC free gap after which the rate fell to 1 CTC per 5 minutes. The rate would then fluctuate wildly between these gap periods. Furthermore there were 4 of these CTC free periods which each ranged from 15 to 25 minutes. When observed at week 5, the CTC rate appeared to gradually rise to its maximum value at approximately 55 CTCs per 5 minutes within 45 minutes and then fall back to 30 CTCs per 5 minutes in 15 minutes. At this time there was only one 5 minute CTC free period after 35 minutes of observation.

     Most studies comparing the number of CTCs in the blood with the survivability of cancer utilize a blood draw. Therefore, most go under the expectation that the concentration of CTCs is constant throughout the bloodstream. However, both the small and large blood vessel tests implied that the CTCs are not uniformly distributed within circulating blood and that their amount is not consistent over a period of time. This is most exemplified by the appearance of CTC free gaps and the rapidly fluctuating nature of the CTC rate. Nonetheless both these traits were suppressed over time for both blood vessel types. At the end of both tests, the CTC rate appeared to fluctuate much more gradually and the number of CTC free periods decreased. Because these traits also appeared in several types of cancer, it is implied that they could be universal to CTCs rather than dependent on one specific type of cancer. However further tests must be done in order to properly enforce this conclusion. Nonetheless, these fluctuations imply that either the CTCs are arrested at certain points in the circulatory system or there are fluctuations in the shedding of CTCs from the primary tumor. These issues could present a problem with CTC studies as they have the potential to skew the number of observable CTCs in a blood draw. However it is possible for this problem to be solved by utilizing larger blood draws. Nevertheless, more tests must be taken in order to validate these claims.


Juratli, Mazen A., Mustafa Sarimollaoglu, Dmitry A. Nedosekin, Alexander V. Melerzanov, Vladimir P. Zharov, and Ekaterina I. Galanzha. “Dynamic Fluctuation of Circulating Tumor Cells during Cancer Progression.” Cancers. 6.1 (2014): 128-142. Web. 27 May 2014.