In some experiments for investigate drug effects for in vivo xenograft model, some authors onle give treatment to the mice for 14 days or 21 days, but the data collection/observation (such as tumor volume and mice body weight)could be done until 35 days or 42 days. Is there any reason for this difference? Or should it be the same time for treatment and observation? Any reference is appreciated.
Dear Iksen!
The difference in the number of days between treatment (administration of drugs) to mice and observation consists in assessing the life span of such animals, in assessing the long-term effects of treatment (if cancer, then - sites and the number of mestats)
Drugs could have effects which last longer than the duration of their administration. In the case of tumor studies, for example, it is important to evaluate whether a treatment is able to permanently eliminate cancerous cells, or only restrain their growth during the treatment course. For this reason you would want to continue monitoring to see if the tumor continued to grow after stopping the treatment course or if it was eliminated entirely and no re-growth occurred.