Eribulin mesylate (iv) will be administered on Day 1 and Day 8 of each cycle (3 weeks as 1 cycle). Trastuzumab (iv) will be administered as weekly use or tri-weekly use. Trastuzumab will be administered immediately after eribulin mesylate administration when used concomitantly.

For DLT evaluation, severity (grade) was classified according to common terminology criteria for adverse events version 4.0 (CTCAE v4.0). DLTs were defined as grade 4 neutropenia persisting for more than 7 days; grade 3 or above febrile neutropenia; grade 4 thrombocytopenia or grade 3 thrombocytopenia requiring blood transfusion; non-hematologic toxicity (excluding toxicity related to neutrophils, leukocytes, lymphocytes, platelets, CD4 lymphocytes, anemia, and bone marrow density) greater than or equal to grade 3 (Exceptions: Dose reduction was not required even when the following conditions were met: grade 3 nausea, vomiting, or diarrhea controllable with anti-emetic or anti-diarrheal medication and abnormal laboratory parameter not requiring treatment); and day 8 administration was delayed or skipped as a result of the subject did not meet the dosing riteria within cycle.

The number of subjects who developed 'treatment-emergent adverse events (AEs) and serious adverse events (SAEs) were evaluated.

Eribulin mesylate (E7389) was administered intravenously on Day 1 and Day 8 of each 3 week cycle. Trastuzumab was administered intravenously weekly, with an initial dose of 4 mg/kg followed by 2 mg/kg for the remaining doses.

For DLT evaluation, severity (grade) was classified according to common terminology criteria for adverse events version 4.0 (CTCAE v4.0). DLTs were defined as grade 4 neutropenia persisting for more than 7 days; grade 3 or above febrile neutropenia; grade 4 thrombocytopenia or grade 3 thrombocytopenia requiring blood transfusion; non-hematologic toxicity (excluding toxicity related to neutrophils, leukocytes, lymphocytes, platelets, CD4 lymphocytes, anemia, and bone marrow density) greater than or equal to grade 3 (Exceptions: Dose reduction was not required even when the following conditions were met: grade 3 nausea, vomiting, or diarrhea controllable with anti-emetic or anti-diarrheal medication and abnormal laboratory parameter not requiring treatment); and day 8 administration was delayed or skipped as a result of the subject did not meet the dosing riteria within cycle.

The DLT analysis set included those participants who received at least one dose of study drug and had a DLT assessment in cycle 1 (3 weeks) without deviations from the eribulin mesylate/trastuzumab dosing regimens and other major protocol prescripts. Participants with a DLT, regardless of this criterion, were also included in the DLT analysis set.

Eribulin mesylate (E7389) was administered intravenously on Day 1 and Day 8 of each 3 week cycle. Trastuzumab was administered intravenously weekly, with an initial dose of 4 mg/kg followed by 2 mg/kg for the remaining doses.