The doctor told her that her child had leukaemia and needed to start treatment immediately.

leukaemia 是医学名词，指"白血病"，由希腊词根 leuk-（白色）和 -emia（血液状况）组成，字面意思是"白血"，指血液中白细胞异常增多的恶性疾病。注意这是英式拼写，美式拼写为 leukemia。