Base game - 144 cards
Campaign box - 55 cards
2 Boss decks of 30 cards per deck - 60 cards
5 characters decks with 15 cards per character - 75
Total - 334 cards
PS: it's possible that I could be wrong though re boss decks.
Your forgot the promos and kickstarer exclusives: 35
One forum member was at the White Wizard Games Fair and played the campaign, there will be probably more cards included than 55.