2686 Apr $13 puts and 1357 $15 calls traded, very large for IMGN. Puts appear to be buy side and new, calls are a mix, don't have enough detail to determine which side, or if this was part of a strategy. Observing what appears to be institutional size put buying. Again, could be hedging a long position in case FDA does something stupid again, or speculation. Just an FYI, not opining.
Large puts bought most likely to protect profit made already since IMGN has been on a recent run. Large call bought most likey in anticipation of price run up to the approval. Feb calls and puts expires before Feb 26th approval date so the logical choice would be to go with April contracts.