An antibody or antigen-binding fragment thereof which specifically binds to all of the following pro/latent TGFβ1 complexes: a TGFβ-GARP complex, a TGFβ1-LTBP1 complex, a TGFβ1-LTBP3 complex and a TGFβ1-LRRC33 complex, and inhibits the release of mature TGFβ1 from the complexes, for use in the treatment of cancer or myelofibrosis in a subject; wherein the antibody or antigen-binding fragment thereof: (a) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SDWIG (SEQ ID NO: 2); CDRH2 comprises the sequence VIYPGDSDTRYSASFQG (SEQ ID NO: 4); CDRH3 comprises the sequence AAGIAAAGHVTAFDI (SEQ ID NO: 6); CDRL1 comprises the sequence KSSQSVLYSSNNKNYLA (SEQ ID NO: 8); CDRL2 comprises the sequence WASTRES (SEQ ID NO: 10); and CDRL3 comprises the sequence QQYYSTPVT (SEQ ID NO: 12); (b) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SYGMH (SEQ ID NO: 1); CDRH2 comprises the sequence VISYDGSNKYYADSVKG (SEQ ID NO: 3); CDRH3 comprises the sequence DIRPYGDYSAAFDI (SEQ ID NO: 5); CDRL1 comprises the sequence TGSSGSIASNYVQ (SEQ ID NO: 7); CDRL2 comprises the sequence EDNQRPS (SEQ ID NO: 9); and CDRL3 comprises the sequence QSYDSSNHGGV (SEQ ID NO: 11); or (c) competes or cross-competes with the antibody defined in part (a) or (b) for binding to TGFβ1 having the amino acid sequence of SEQ ID NO: 21; wherein the antibody or antigen-binding fragment thereof does not bind TGFβ2 having the amino acid sequence of SEQ ID NO: 22 or TGFβ3 having the amino acid sequence of SEQ ID NO: 23. wherein the antibody or antigen-binding fragment thereof: (a) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SDWIG (SEQ ID NO: 2); CDRH2 comprises the sequence VIYPGDSDTRYSASFQG (SEQ ID NO: 4); CDRH3 comprises the sequence AAGIAAAGHVTAFDI (SEQ ID NO: 6); CDRL1 comprises the sequence KSSQSVLYSSNNKNYLA (SEQ ID NO: 8); CDRL2 comprises the sequence WASTRES (SEQ ID NO: 10); and CDRL3 comprises the sequence QQYYSTPVT (SEQ ID NO: 12); (b) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SYGMH (SEQ ID NO: 1); CDRH2 comprises the sequence VISYDGSNKYYADSVKG (SEQ ID NO: 3); CDRH3 comprises the sequence DIRPYGDYSAAFDI (SEQ ID NO: 5); CDRL1 comprises the sequence TGSSGSIASNYVQ (SEQ ID NO: 7); CDRL2 comprises the sequence EDNQRPS (SEQ ID NO: 9); and CDRL3 comprises the sequence QSYDSSNHGGV (SEQ ID NO: 11); or (c) competes or cross-competes with the antibody defined in part (a) or (b) for binding to TGFβ1 having the amino acid sequence of SEQ ID NO: 21; (a) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SDWIG (SEQ ID NO: 2); CDRH2 comprises the sequence VIYPGDSDTRYSASFQG (SEQ ID NO: 4); CDRH3 comprises the sequence AAGIAAAGHVTAFDI (SEQ ID NO: 6); CDRL1 comprises the sequence KSSQSVLYSSNNKNYLA (SEQ ID NO: 8); CDRL2 comprises the sequence WASTRES (SEQ ID NO: 10); and CDRL3 comprises the sequence QQYYSTPVT (SEQ ID NO: 12); CDRH1 comprises the sequence SDWIG (SEQ ID NO: 2); CDRH2 comprises the sequence VIYPGDSDTRYSASFQG (SEQ ID NO: 4); CDRH3 comprises the sequence AAGIAAAGHVTAFDI (SEQ ID NO: 6); CDRL1 comprises the sequence KSSQSVLYSSNNKNYLA (SEQ ID NO: 8); CDRL2 comprises the sequence WASTRES (SEQ ID NO: 10); and CDRL3 comprises the sequence QQYYSTPVT (SEQ ID NO: 12); (b) comprises a heavy chain variable region comprising a CDRH1, CDRH2, and CDRH3 and a light chain variable region comprising a CDRL1, CDRL2, and CDRL3, wherein: CDRH1 comprises the sequence SYGMH (SEQ ID NO: 1); CDRH2 comprises the sequence VISYDGSNKYYADSVKG (SEQ ID NO: 3); CDRH3 comprises the sequence DIRPYGDYSAAFDI (SEQ ID NO: 5); CDRL1 comprises the sequence TGSSGSIASNYVQ (SEQ ID NO: 7); CDRL2 comprises the sequence EDNQRPS (SEQ ID NO: 9); and CDRL3 comprises the sequence QSYDSSNHGGV (SEQ ID NO: 11); or CDRH1 comprises the sequence SYGMH (SEQ ID NO: 1); CDRH2 comprises the sequence VISYDGSNKYYADSVKG (SEQ ID NO: 3); CDRH3 comprises the sequence DIRPYGDYSAAFDI (SEQ ID NO: 5); CDRL1 comprises the sequence TGSSGSIASNYVQ (SEQ ID NO: 7); CDRL2 comprises the sequence EDNQRPS (SEQ ID NO: 9); and CDRL3 comprises the sequence QSYDSSNHGGV (SEQ ID NO: 11); or (c) competes or cross-competes with the antibody defined in part (a) or (b) for binding to TGFβ1 having the amino acid sequence of SEQ ID NO: 21; wherein the antibody or antigen-binding fragment thereof does not bind TGFβ2 having the amino acid sequence of SEQ ID NO: 22 or TGFβ3 having the amino acid sequence of SEQ ID NO: 23.