死因は

the cause of death

→ 死因
phrase Rare #23,719
the cause of death は marks 死因 as the topic. In a question, this asks what the cause of death was.
JA: 彼女の死因は何ですか?
EN: What was her cause of death?

今家族に連絡を、死因は?

Contact the family now. What was the cause of death?

— ベイビー・ブローカー (2022)

ココ死因は?

Coco, what was the cause of death?

— ブレードランナー 2049 (2017)

夫の死因は無関係

Her husband's cause of death is irrelevant.

— 落下の解剖学 (2023)

トムの死因は未だに謎に包まれている。

The cause of Tom's death is still shrouded in mystery.

叔父の死因は癌だったそうです。

I heard that my uncle died of cancer.

死因は心臓発作だった。

The cause of death was a heart attack.

彼の死因はガンだった。

His cause of death was cancer.

グリンダの死因は??

What was the cause of Glinda’s death??

— ウィキッド ふたりの魔女 (2024)