Translation guide
The English word "malignant" is most commonly used in medical contexts to describe a disease, especially cancer, that is severe, progressive, and life-threatening. It can also be used figuratively to describe a person or influence that is harmful or malevolent. This guide focuses on the medical sense, which is the most frequent use, and briefly covers the figurative sense.
Describing a tumor, disease, or condition that is cancerous, invasive, and likely to cause death if untreated.
The standard medical term for 'malignant'. Used as a noun or adjective (often with の). Commonly paired with 腫瘍 (tumor) or 疾患 (disease).
Describing a person, influence, or action that is evil, spiteful, or intended to cause harm.
Literally 'having ill will'. The most natural way to express 'malignant' in a figurative sense, meaning intentionally harmful or malevolent.
彼の悪意のある噂が広まった。
His malignant rumors spread.
In medical contexts, 悪性 (malignant) is the opposite of 良性 (りょうせい, benign). For example, 良性腫瘍 is a benign tumor. These terms are standard in Japanese medicine.
Do not use 悪性 for figurative meanings like 'malignant person' or 'malignant influence'. 悪性 is strictly medical. Use 悪意のある or 邪悪な instead.
悪性腫瘍が見つかりました。
A malignant tumor was found.
この病気は悪性です。
This disease is malignant.
Adjectival form of 悪性, used directly before nouns. Very common in medical contexts.
悪性の腫瘍は転移する可能性があります。
Malignant tumors can metastasize.
Refers to the grade or degree of malignancy, often used in pathology reports.
悪性度の高いがんです。
It's a high-grade malignant cancer.
While 'cancer' is not a direct translation of 'malignant', it is often used in Japanese where English would say 'malignant tumor'. Note: がん can refer to cancer in general, not always specifying malignancy, but context usually makes it clear.
Use 悪性 to explicitly state malignancy; がん alone may not always convey the severity.
がんと診断されました。
I was diagnosed with cancer (malignant).
Means 'evil' or 'wicked'. Stronger than 悪意のある, often used for inherently evil characters or forces.
邪悪な影響を与える人物だ。
He is a malignant influence.
Means 'harmful' or 'toxic'. Can be used for influences or environments, but lacks the intentional malice of 'malignant'.
This is a broader term for 'harmful'; use 悪意のある if you want to emphasize intent.
有害な思想が広がっている。
Malignant ideas are spreading.