In general, avoid any countries that require live vaccines to go to if you're having chemo as they are contraindicated.
You should also avoid countries if:
• The healthcare system is limited or a long journey away
• The temperature is very hot. This can lead to dehydration and DVT risk
• Very sunny climes due to possible photosensitivity from chemotherapy
• Countries that are not covered by the EHIC or reciprocal health arrangements such as the USA