Cell Kinetics and Epidermal Growth Factor Receptor Expression: Useful Guides in Esophageal Cancer?
Radiotherapy and chemotherapy both cause cell death in tumors as well as in normal tissues. As soon as a certain level of damage is reached in the tissue, repopulation starts via feedback mechanisms. In fast proliferating tissues like skin and intestinal epithelia, this compensatory proliferation starts within 2–3 weeks. Compensatory proliferation is not linear but increases exponentially as a function of the overall treatment time [1,2]. This repopulation can influence the effect of protracted irradiation to a large extent. When the overall treatment time is shortened from 7 to 2 weeks, the tolerance of the acutely responding tissues decreases to such a degree that the total dose must be reduced from 70 to 50 Gy. Probably similar effects occur in fast proliferating tumors. By this mechanism the therapeutic effect of extremely protracted irradiation is jeopardized [3, 4]. It has been described in head and neck cancer that local tumor control did decrease from 86% to 32% when treatment was protracted from 35 days to 50 days or more . Hence the rationale for shortening overall treatment time for fast proliferating tumors to counteract repopulation. Preliminary results of the European Organization for Research and Treatment of Cancer (EORTC) trial for head and neck tumors indeed show that local tumor control in fast proliferating tumors is higher after accelerated radiotherapy (70Gy/5 weeks) compared to conventional irradiation (70Gy/7 weeks) . This remains to be assessed for esophageal tumors, especially for squamous esophageal cancer which is histologically comparable with head and neck cancer.
KeywordsEpidermal Growth Factor Receptor Epidermal Growth Factor Receptor Expression Local Tumor Control Cell Kinetic Compensatory Proliferation
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