That's entirely possible and the best explanation I've read yet why a " watch & wait" might be appropriate, to see if such a major surgery is really in her best interests (given how arduous and challenging recovery will be as well as the surgery risks themselves), or if surgery will be unlikely to improve her prognosis (if the "wait" shows significant metastases elsewhere or tumour growth). Perhaps his concern is recovery could interfere with any treatment/surgery for any cancer elsewhere.
Maybe his news was good in that treatment has affected the original mass based on scans and biopsies. But maybe notwithstanding that, he remains guarded that a pelvic exenteration is worth the surgical risks/recovery and impact if the cancer has already advanced beyond the pelvic region. Perhaps his wait is to see if any microscopic advancement is actually occurring elsewhere in her body that has not yet been picked up. In 6 weeks, it's more likely to be viewable. But, it also leaves the risk of being inoperable too if they find significant growth.
In that light, his comments, and the oncologist's agreement, begin to make some sense.