악성이 · 악성을
malignancy; malignant, vicious (often used before a noun)
Example
검사 결과 악성 종양으로 밝혀졌어요.
The test results showed that it was a malignant tumor.
Word parts
악 bad+성 nature
Literally 'bad nature'.
Good to know
Outside medicine, 악성 means vicious: 악성 댓글 (악플, hate comments), 악성 코드 (malware).
Related words