Horn-like thing on tomatoes

Hi all!

I planted seven different varieties of tomatoes this year:

1. Sungold - indeterminate cherry.
2. Green Grape - indeterminate, small-kiwi shaped fruit.
3. Matt's Wild Cherry
4. Kuralik - determinite cherry.
5. Mr. Stripey - indeterminate green with yellow stripes.
6. Sweet Million - indeterminate cherry.
7. Black Prince - indeterminate dark red-black fruit.

Of all of them, Sungold is the only one that's thriving. Black Prince is living, but not fruiting anymore. Green Grape looks okay. The rest have either died or are in the process of dying. The leaves start curling up, then the veins get dark, then the leaves start yellowing. The plant stops growing, then the whole thing kind of wastes away.

My concern is with the Black Prince tomatoes. A few of the fruit have a horn-shaped projection sticking out of them. They literally look like they sprouted a horn from the skin of the tomato. Does anyone know what this is?

If it helps, I live in the Seattle area.

Thanks! OTM.