CPT-11 (Irinotecan) and Radiation Side Effects

John Han-Chih Chang, MD and Kenneth Blank, MD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
Does radiation in the pelvic area prevent the use of CPT-11? My wife is a stage 4 cancer patient and has received FUDR, FUDR and Leucovorin, then FUDR, Leucovorin and Gemzar^®. She was allergic to the Gemzar and was due to start the CPT-11 when she developed a mass in her pelvic area that requires radiation before she can continue any more chemotherapy.
TN

John Han-Chih Chang, MD and Kenneth Blank, MD, Editorial Assistants for Oncolink, respond:

Dear TN,
Thank you for your interest and question.

The chemotherapy agent (CPT-11) you are talking about is also called Irinotecan. It is a Topoisomerase I (Topo I) inhibitor similar to Topotecan and 9-aminocamptothecin. Topo I assists the cell during replication. Inhibition of this enzyme causes problems with cell reproduction and ultimately tumor growth. These types of chemotherapeutic agents have been used for brain gliomas, cervix cancers, lung cancers, etc?

There is some preliminary data with Topo I inhibitors that suggest that they cause increased sensitization of tissues to radiation damage. Thus, the rationale behind doing radiation before starting the CPT-11 is that there could be unwanted increased side effects from the radiation therapy if it was given concurrently (with the CPT-11). Using CPT-11 with radiation therapy could perhaps increase the radiation damage to the cancerous tumor. Our experience is too limited at this time with CPT-11 to believe that the benefit of increased cancer killing will far outweigh the potential risk of increased side effects from pelvic radiation (which can be quite difficult to manage).