"Pity" is "a feeling of sadness or sympathy for someone else's unhappiness or difficult situation". When we describe something as "shame", it is something that "is disappointing or not satisfactory". It can also mean "an uncomfortable feeling of guilt or of being ashamed because of your own or someone else's bad behavior". As far as I'm aware "it's a shame" and "it's a pity" are interchangeable. Just remember that shame and pity have slightly different meanings, though. (the definitions aren't my own, but are from the Cambridge dictionary)