After my uncle was diagnosed with cancer, the family immediately took him to see an oncologist.

oncologist 是由词根 onco-（表示"肿瘤"）和后缀 -logist（表示"专家、学者"）组成的复合词，指专门研究、诊断和治疗肿瘤的医生，即"肿瘤科医生"。