〜にしても
even if, even allowing for; whether … or
Noun / Plain form + にしても · Aにしても Bにしても
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にしても grants a point, then says it doesn't change the conclusion: 冗談にしても、言いすぎだ, "even as a joke, that's going too far". 忙しいにしても、電話ぐらいはできるでしょう, "even if you're busy, you can at least call".
Doubled, it means "whether … or": 参加するにしても、しないにしても、返事をください, "whether you're coming or not, please reply".
The set phrase それにしても means "even so" or "all the same", and often introduces a sudden comment: それにしても、暑いですね, "still, it's awfully hot, isn't it?"
In formal writing, にしろ and にせよ mean the same. Compare にしては, "considering", which it looks very like but doesn't mean.
Examples
冗談にしても、言いすぎだ。
Even as a joke, that's going too far.
忙しいにしても、電話ぐらいはできるでしょう。
Even if you're busy, you can at least call.
参加するにしても、しないにしても、返事をください。
Whether you're coming or not, please reply.
遅れるにしても、連絡してほしかった。
Even if you were going to be late, I wish you'd let me know.
それにしても、暑いですね。
Still, it's awfully hot, isn't it?