A conjugated activatable antibody comprising the structure of Formula (I) or a salt thereof: (a) wherein (i) AB is an antibody that specifically binds to human CD71 and comprises i. a heavy chain variable region comprising a CDRH1 sequence comprising SEQ ID NO: 9, a CDRH2 sequence comprising SEQ ID NO: 10, and a CDRH3 sequence comprising SEQ ID NO: 11; and ii. a light chain variable region comprising a CDRL1 sequence comprising SEQ ID NO: 12 or SEQ ID NO:13, a CDRL2 sequence comprising SEQ ID NO: 14, and a CDRL3 sequence comprising SEQ ID NO: 15; (ii) MM is a masking moiety comprising the amino acid sequence of SEQ ID NO: 18, wherein the MM inhibits the binding of the AB to human CD71 when the conjugated activatable antibody is in an uncleaved state; (iii) LP1 is a first linking moiety comprising the amino acid sequence of SEQ ID NO: 207; (iv) CM is a cleavable moiety comprising the sequence of SEQ ID NO: 156, wherein the CM is a polypeptide that functions as a substrate for a protease; and (v) LP2 is a second linking moiety comprising the amino acid sequence of SEQ ID NO: 38; and (b) wherein "n" is 2. (a) wherein (i) AB is an antibody that specifically binds to human CD71 and comprises i. a heavy chain variable region comprising a CDRH1 sequence comprising SEQ ID NO: 9, a CDRH2 sequence comprising SEQ ID NO: 10, and a CDRH3 sequence comprising SEQ ID NO: 11; and ii. a light chain variable region comprising a CDRL1 sequence comprising SEQ ID NO: 12 or SEQ ID NO:13, a CDRL2 sequence comprising SEQ ID NO: 14, and a CDRL3 sequence comprising SEQ ID NO: 15; (ii) MM is a masking moiety comprising the amino acid sequence of SEQ ID NO: 18, wherein the MM inhibits the binding of the AB to human CD71 when the conjugated activatable antibody is in an uncleaved state; (iii) LP1 is a first linking moiety comprising the amino acid sequence of SEQ ID NO: 207; (iv) CM is a cleavable moiety comprising the sequence of SEQ ID NO: 156, wherein the CM is a polypeptide that functions as a substrate for a protease; and (v) LP2 is a second linking moiety comprising the amino acid sequence of SEQ ID NO: 38; and (i) AB is an antibody that specifically binds to human CD71 and comprises i. a heavy chain variable region comprising a CDRH1 sequence comprising SEQ ID NO: 9, a CDRH2 sequence comprising SEQ ID NO: 10, and a CDRH3 sequence comprising SEQ ID NO: 11; and ii. a light chain variable region comprising a CDRL1 sequence comprising SEQ ID NO: 12 or SEQ ID NO:13, a CDRL2 sequence comprising SEQ ID NO: 14, and a CDRL3 sequence comprising SEQ ID NO: 15; i. a heavy chain variable region comprising a CDRH1 sequence comprising SEQ ID NO: 9, a CDRH2 sequence comprising SEQ ID NO: 10, and a CDRH3 sequence comprising SEQ ID NO: 11; and ii. a light chain variable region comprising a CDRL1 sequence comprising SEQ ID NO: 12 or SEQ ID NO:13, a CDRL2 sequence comprising SEQ ID NO: 14, and a CDRL3 sequence comprising SEQ ID NO: 15; (ii) MM is a masking moiety comprising the amino acid sequence of SEQ ID NO: 18, wherein the MM inhibits the binding of the AB to human CD71 when the conjugated activatable antibody is in an uncleaved state; (iii) LP1 is a first linking moiety comprising the amino acid sequence of SEQ ID NO: 207; (iv) CM is a cleavable moiety comprising the sequence of SEQ ID NO: 156, wherein the CM is a polypeptide that functions as a substrate for a protease; and (v) LP2 is a second linking moiety comprising the amino acid sequence of SEQ ID NO: 38; and (b) wherein "n" is 2. <EOS>