Which sentences are correct? Thanks.
Our company has suffered from lack of investment.
Our company has suffered lack of investment.
He was eventually diagonosed as suffering from terminal cancer.
He was eventually diagonosed as suffering terminal cancer.
Which sentences are correct? Thanks.

Question

Answer

Yes, #1 and #3 are correct. You can use "suffer" without "from" in the narrow sense of "to tolerate":

I suffered his insults to get the promotion
The climbers suffered the cold to get to the top of the mountain

However in your contexts you defnitely need "from"

Answer

The first and third sentences are correct.

Answer

from is preferable - but any of these sentences works...