The present invention generally relates to the fields of cancer therapy and cancer prevention. More particularly, the present invention generally relates to a diagnostic marker for predicting the efficacy of topoisomerase I (topo I) inhibitors in the treatment of cancers. More specifically, the present invention relates to methods, machines, computer systems, computable readable media and kits which can be used to identify and determine the effectiveness of topoisomerase I (topo I) inhibitors in the treatment of cancers, and in some embodiments, the level of sensitivity or resistance of a tumor cell to a topoisomerase I inhibitor, such as camptothecin (CPT), or CTP analogues such as topotecan and irinotecan and derivatives thereof. More specifically, the present invention related to methods, machines, computer systems, computable readable media and kits which can be used to determine the presence of phosphorylation of topoisomerase I polypeptide, in some embodiments phosphorylation at residue serine 10 (S10) of a topoisomerase I polypeptide, wherein the presence of phosphorylation, in particular the phosphorylation at serine 10 of a topoI polypeptide indicates a cancer is likely to be unresponsive to a topo I inhibitor, whereas the absence of phosphorylation, in particular, the absence of phosphorylation at residue serine 10 (S10) identifies a cancer is likely to be responsive to a topo I inhibitor. Other aspect of the present invention relate to phospho-serine 10 topoisomerase I antibodies and other protein binding moieties, and uses thereof.
