Answer: What you describe sounds like catfacing, a common disorder of tomatoes. Catfacing is caused by poor pollination. This is associated with very cool or very hot temperatures and results in swollen areas developing on the blossom end of the fruit. The crevices between the swellings become dry.
To control, you might try organic mulch over the soil surface. This can moderate temperatures. Be sure to grow the tomato crop during the appropriate season. Remove damaged fruits so that they do not draw any more energy from the vine. Future tomatoes may or may not be damaged, depending on temperatures during fruit set.
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