Conjugate for targeting therapeutic or diagnostic agent or drug to cells or tissues in a body, e.g. areas of neoplastic growth or angiogenesis. Use of conjugate for in vivo diagnosis or therapy e.g. inhibiting tumor growth or metastasis, inhibiting angiogenesis and/or treating cancer. Conjugate comprises therapeutic or diagnostic agent as oligomeric protein e.g. heterodimeric protein, wherein first and second subunits of protein are each conjugated to a specific binding member e.g. an antibody fragment such as scFv. Subunits of oligomer may be conjugated to specific binding members as fusion proteins. Conjugate may comprise IL-12 heterodimer having two subunits, each subunit fused to scFv L19 or TN11 for targeting IL-12 to extracellular matrix components associated with neoplastic growth and angiogenesis.