Thank you for using Ask an Expert for help with your mutant tomatoes. Well, they are probably not actual mutants.
I believe that your tomatoes are experiencing “catfacing”. I have included photos of this phenomenon for comparison.
There is little definitive research into this issue; but it has been connected with several environmental conditions that your garden may be experiencing. Under conditions of extreme heat, pollination of the flowers is disturbed, the production of natural plant hormones is disrupted, and the resulting fruit do not develop normally. When the vines are exposed to a wide difference in day and night temperatures, a similar effect occurs.
Other associations with catfacing are heavy pruning of the vines, high levels of nitrogen fertilizer, severe drought, and indeterminate varieties (Stupice is one of these).
Feel free to eat these weather-affected tomatoes. The fruit value is not reduced, though it can be difficult to recover some around the deformation.
Have a good gardening year,