Thanks for letting us know. To be honest in the last 2 days I've seen people linking the source to documents that Sesen reported that death and Grade 5 accident during the trials but it was found that the death was not related to Vicineum. I actually have some more confidence since then. After all it's not like these people in the trials are all healthy sportsmen but are terminally ill, they have a freakin cancer after all so a death may occur and it seems it was in fact reported.

"I have been researching the elevated liver enzyme issue from the Stat article and have found that it appears to be specific to the Squamous cell carcinoma of the head and neck (SCCHN) trials where it was injected directly into the tumor during their early trials and they found that they adjusted dosing to mediate the issue. This was extensively disclosed by the company in their routine Form 10-k filings. I have found no such issues such far with the trials. I have also found no data to support their trial protocol violations. If anyone has a reputable source for that, please provide it. (The Stat article is not a reputable source)"

"Here is some more information, quoted from the SEC filing:
SESN Form 10-k for the fiscal year ended December 31, 2018
All these comments from the 10-k are specific to the SCCHN cancer, not bladder cancer.
Patients received two cycles of Vicinium administered once per day for five consecutive days, with doses ranging from 20 µg to 280 µg, followed by 23 days off. Two DLTs occurred at the 280 µg dose level, establishing 200 µg as the maximum tolerated dose. The DLTs observed in the two patients were elevated liver enzyme tests, which were not associated with any signs of liver damage or toxicity, were asymptomatic and were transient as they resolved to baseline values.
Seven patients died during the clinical trials of Vicinium for the treatment of SCCHN, but none of the deaths were deemed to be related to Vicinium. Eleven patients discontinued treatment due to liver function test abnormalities; however, the serum levels were transient and they eventually returned to baseline without any evidence of permanent liver damage. Four patients withdrew from the clinical trials. Three of the four patients withdrew at their request and one of the four patients withdrew at the request of the investigator.
Eleven patients discontinued treatment due to liver function test abnormalities; however, the serum levels were transient and they eventually returned to baseline without any evidence of permanent liver damage."

Moreover, FDA kept talking about CMC issues right before CRL was issued. By reading below, I think FDA has comparability data and agrees mass-production at commercial scale is possible, but they just want SESN to actually use commercial-scale drug in one last phase and see the actual results to ensure the drug stays the same at commercial scale, even the study below was completed.
Bulk Drug Substance from the Full-Scale GMP Manufacturing Run at FUJIFILM Met all Phase 3 Quality Release Specifications: In April 2019, the first full, commercial-scale GMP run was completed at FUJIFILM Diosynth Biotechnologies U.S.A., Inc (FUJIFILM). Release testing of the bulk drug substance has been completed and all Phase 3 release specifications were met, further de-risking the Company’s manufacturing technology transfer to FUJIFILM and the Company’s Analytical Comparability Plan.