Cancer affects about 1 out of 1000 pregnancies with the most common malignancies being breast cancer, melanoma and haematological malignancies. The evidence-based data on cancer treatment and its effects for a mother and her fetus is limited but preliminary data suggest that in some circumstances cancer treatment and healthy fetal development can be compatible. However, maternal cancer treatment exposes the fetus to the side effects of varying degrees, which cannot always be determined in advance. Uncertainty could lead to disagreements on whose interest should prevail and how much uncertainty is acceptable in an individual situation. Current approaches tend to combine the respect for maternal autonomy and ‘seeing fetus as a patient’ when offering ethical guidance to healthcare professionals. Meanwhile, support services for patients remain limited. In cancer during pregnancy, care patient support services should recognize the importance of relationships between affected stakeholders.