Photo: Sang Tan, AP, from USA Today article
USA Today is a strange place to get news about mass spectrometry devices, but this one is novel enough for the mainstream media. Apparently, it is common practice to cauterize tissue after cancer removal.
The new "smart knife" is connected to a small MS device that is loaded with cancer profiles. The smoke arising from the cauterized tissue is then compared to these profiles to determine whether the tissue is more like normal cells or the cancerous ones.
There isn't much more info than this in the USA Today article, but there is loads of info in the original article at Science Translational Medicine.