Abstract: The present invention refers to an in vitro method for determining the efficacy of anti-HER2 therapy in the absence of chemotherapy in a patient with HER2+ breast cancer comprising the detection and/or quantification of the expression of HER2 in an isolated biological sample of the patient, either (1) before or (2) before and during the anti-HER2 therapy in the absence of chemotherapy treatment. The present invention also refers to the use of a gene expression product of HER2 as a as an in vitro marker for determining the efficacy of anti-HER2 therapy in the absence of chemotherapy in a patient with HER2+ breast cancer, or alternatively as an in vitro marker for deciding or recommending whether to initiate an alternative medical regime to anti-HER2 therapy without chemotherapy in a patient with HER2+ breast cancer.

Abstract: The present invention relates to a method of diagnosis and therapy of cancers expressing the HER2 receptor. The invention provides antibodies or fragments thereof that recognise an epitope of the HER2 receptor truncated form CTF-611, said epitope being defined by a sequence included in SEQ ID NO: 2, and that are capable of discriminating between CTF-611 and CTF-616 (represented by SEQ ID NO:7), preferably additionally capable of discriminating between CTF-611 and CTF-613 (represented by SEQ ID NO:6). The invention also provides a method of cancer diagnosis using the disclosed antibodies, which comprises the detection of the presence of the HER2 receptor truncated form consisting of the amino acid sequence SEQ ID NO: 1 in a patient sample.