Ewing's tumour vs Ewing's tumor

Ewing's tumour and Ewing's tumor both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ewing's tumour	Yes	No	No	No
Ewing's tumor	Yes	No	No	No

As nouns, Ewing's tumour and Ewing's tumor are synonyms defined as:

Ewing's tumour and Ewing's tumor: malignant tumor in bone marrow (usually in the pelvis or in long bones)

Other synonyms of Ewing's tumour include endothelial myeloma, Ewing's sarcoma.

Ewing's tumour (noun)	Ewing's tumor (noun)
malignant tumor in bone marrow (usually in the pelvis or in long bones)	malignant tumor in bone marrow (usually in the pelvis or in long bones)