Study of Prophylactic Octreotide to Prevent or Reduce the Frequency and Severity of Diarrhoea in Subjects Receiving Lapatinib With Capecitabine for the Treatment of Metastatic Breast Cancer

Inclusion Criteria:

* Signed written informed consent
* Histologically or cytologically confirmed HER2-positive advanced or metastatic breast cancer which has progressed following prior therapy, which must have included anthracyclines and taxanes and therapy with trastuzumab in the metastatic setting
* Females age \>=18 years old
* Eastern Cooperative Oncology Group (ECOG) performance status 0-2
* Life expectancy of at least 12 weeks
* Able to swallow and retain oral medications
* Incapable of becoming pregnant, or not pregnant and using an adequate form of contraception, i.e. a female who is of:

  1. non-childbearing potential (physiologically incapable of becoming pregnant), including any female who has had hysterectomy, bilateral oophorectomy, bilateral tubular ligation or is post-menopausal (total cessation of menses for at least 1 year);
  2. childbearing potential must have a negative serum pregnancy test within 7 days prior to treatment with Octreotide if randomised to receive Octreotide or the first dose of Lapatinib with Capecitabine if randomised to receive no Octreotide, preferably as close to the first dose as possible, and must agree to use adequate contraception (intrauterine device, birth control pills unless clinically contraindicated, or barrier device) and other acceptable contraceptive methods during the study and continuing for at least 4 weeks after the final dose of treatment with Lapatinib and Capecitabine
* Subjects must complete all screening assessments as outlined in the protocol
* Subjects must complete the Functional Assessment of Chronic Illness Therapy-Diarrhoea (FACIT-D) and diarrhoea diary before receiving the first dose of Octreotide if randomised to receive Octreotide. All subjects must complete the FACIT-D and diarrhoea diary before receiving the first dose of Lapatinib with Capecitabine
* Prior treatment with other chemotherapeutic agents or endocrine therapy is permitted. All prior treatment related toxicities, except diarrhoea and alopecia, must be National Cancer Institute common terminology criteria for adverse events (NCI CTCAE) (version 4.03)\<= Grade 1 at the time of randomization.Subjects with diarrhoea with any grade of severity within 14 days prior to randomisation are excluded from LAP117314
* Prior treatment with radiation therapy is permitted provided that at least 2 weeks have elapsed since the last fraction of radiation therapy prior to treatment with Octreotide if randomised to receive Octreotide or the first dose of Lapatinib with Capecitabine if randomised to receive no Octreotide, and all radiation therapy related AEs are \<= Grade 1 at the time of randomization
* French subjects: In France, a subject will be eligible for inclusion in this study only if either affiliated to or a beneficiary of a social security category

Exclusion Criteria:

* Concurrent treatment with an investigational agent or concurrent participation in another clinical study
* Administration of an investigational drug within 30 days or 5 half-lives, whichever is longer, prior to treatment with Octreotide for subjects randomised to receive Octreotide or the first dose of Lapatinib and Capecitabine for subjects randomised to receive no Octreotide
* Treatment with Octreotide within the 3 months prior to randomization
* Concurrent chemotherapy, radiation therapy, immunotherapy, biologic therapy (including an Epidermal growth factor receptor (EGFR) and/or HER2 inhibitor), or hormonal therapy for treatment of cancer
* Dementia, altered mental status, or any psychiatric condition that would prohibit the understanding or rendering of informed consent, unless a legally acceptable representative could provide informed consent (if in accordance with the policies of the local Ethics Committee)
* Concurrent disease or condition that would make the subject inappropriate for study participation or any serious medical or psychiatric disorder that would interfere with the subject's safety or compliance with study procedures
* Diarrhoea with any grade of severity within 14 days prior to treatment with Octreotide for subjects randomised to receive Octreotide or within 14 days prior to the first dose of Lapatinib and Capecitabine for subjects randomised to receive no Octreotide
* Malabsorption syndrome, inflammatory bowel disease (ulcerative colitis, Chrohn's disease), irritable bowel syndrome, disease significantly affecting gastrointestinal function, or resection of the stomach or small bowel
* Pregnant or lactating subjects
* Prior treatment with Lapatinib
* French subjects: the French subject has participated in any study using an investigational drug during the previous 30 days or 5 half-lives, whichever is longer, preceding the first dose of protocol treatment