| Cover | Jul. 15, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Entity Registrant Name | SESEN BIO, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36296 |
| Entity Tax Identification Number | 26-2025616 |
| Entity Address, Address Line One | 245 First Street |
| Entity Address, Address Line Two | Suite 1800 |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02142 |
| City Area Code | 617 |
| Local Phone Number | 444-8550 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 |
| Trading Symbol | SESN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001485003 |
| Amendment Flag | true |
| Document Period End Date | Jul. 15, 2022 |
