Tumour escape

Although immune surveillance is certainly responsible for the detection and eradication of some transformed cells, the prevalence of cancer indicates that this surveillance is nowhere near 100 per cent effective. Some transformed cells obviously display characteristics that allow them to evade this immune surveillance. The exact molecular details of how such tumour escape is achieved remains to be confirmed, although several mechanisms have been implicated, including ... 

Whatever the exact nature of tumour escape, it has been demonstrated, both in vitro and in vivo, that immunostimulation can lead to enhanced tumour detection and destruction. Several approaches to cancer immunotherapy have thus been formulated, many involving application of IL-2 as the primary immunostimulant. 

Vicari AP, Caux C, Trinchieri G. Tumour escape from immune surveillance through dendritic cell inactivation. Semin Cancer Biol 2002 12 33—42. 

Naturally occurring tumours evoke little or no immune response in experimental animals. This is disappointing but it must be remembered that these cells have already escaped the normal immune surveillance. 

Benign tnmonrs are nsnally only a problem when they impair the fnnction of organs or canse metabolic stress. They can be removed by snrgery or radiation therapy. Malignant tnmonrs are mnch more of a problem, since the cells can escape from the primary tnmonr to other sites in the body, where they settle and develop into secondary tumours (metastases). Then, chemotherapy is the only treatment available. The process is known as metastasis. 

Friedl, P. and Wolf, K., Tumour-cell invasion and migration Diversity and escape mechanisms, Nat. Rev. Cancer, 3, 362-374, 2003. 

Zhu and Zhao prepared pH-sensitive polymeric vesicular aggregates using combshaped amphiphilic polymers, i.e., cholate grafted poly(L-lysine) (PLL-CA), with an amphiphilic PEG-doxorubicin (DOX) conjugate (Figure 2.11) [57c]. The pH sensitivity leads to better uptake of the vesicles by cancer cells (MCF-7) under conditions close to the extracellular environment of a solid tumour (pH = 6.5) and subsequent escape from endosomes after endocytosis. Moreover, if the pH value is lower the vesicles destabilise. 

Our own body disposes of a perfect homing system immune cells specifically recognize and destroy foreign material as well as tumour cells. Although these may escape the immune surveillance, it is fascinating to watch them being attacked by lymphocytes (a class of immune cells). 

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