The use of the term gospel in Paul.
The good news as preached by Paul.
Romans 1.1, 9, 16; 2.16; 10.16; 11.28; 15.16, 19; 16.25;
...and in the following (from the spurious epistles):
Ephesians 1.13; 3.6; 6.15, 19;
The LXX contains only one instance of this noun (2 Samuel 4.10).
Additionally, Paul uses the verb ευαγγελιζω (to preach, preach the gospel, or evangelize) in the following passages from the genuine epistles:
In the spurious epistles this verb appears only in Ephesians 2.17; 3.8. In the rest of the canonical epistles and the apocalypse it appears only in Hebrews 4.2, 6; 1 Peter 1.12, 25; 4.6; Revelation 10.7; 14.6.
The LXX contains many more instances of this verb than of the corresponding noun.
In all of the Pauline instances of the verb or the noun, with the exception of 1 Thessalonians 3.6, the gospel in question appears to be the good news about Jesus Christ. Even when he quotes from the LXX (in which case the original sense would not have been the gospel of Jesus Christ) he appears to be applying the verse to his gospel.
The Priene calendar inscription intriguingly calls the birth of Caesar Augustus good news (in the plural, ευανγελιων).