Inclusion Criteria:

- Age >=18 years

- KPS performance status >= 70%

- For the Phase 1 portion of the trial, all patients must have a histologically
confirmed solid tumor malignancy. For the Phase 2 portion of the trial, patients
must have metastatic breast cancer with HER2 amplification by FISH or 3+ HER2
overexpression by immunohistochemistry ("IHC") Patients may have had either
progressive disease within 3 months following last dose of adjuvant treatment with
trastuzumab OR progressive disease following initial therapy for metastatic disease
with trastuzumab (trastuzumab may have been administered with cytotoxic chemotherapy,
hormonal therapy or as single agent.) Patients who have received trastuzumab single
agent therapy (without documented progressive disease) followed by trastuzumab
combination therapy remain eligible for this study at the time of disease
progression. Patients must have measurable disease by RECIST

- All Adverse Events of any prior chemotherapy, surgery, or radiotherapy, must have
resolved to NCI CTCAE (v. 3.0) Grade <= 2 (except for alopecia)

- The following laboratory results, within 10 days of KOS-953 administration:

- Hemoglobin >= 8.5 g/dL

- Absolute neutrophils count >= 1.5 x 10*9* /L

- Platelet count >= 75 x 10*9* /L

- Serum bilirubin <= 2 x ULN

- AST and ALT <= 2 x ULN

- Serum creatinine <= 2 x ULN

- Signed informed consent

Exclusion Criteria:

- Documented hypersensitivity reaction of CTCAE Grade >= 3 to prior therapy containing
Cremophor (for those patients who receive the Tanespimycin Injection only) or
Herceptin

- Pregnant or breast-feeding women

- Known active CNS metastases

- Except for trastuzumab (Herceptin®) administered between 7-21 days prior to first
tanespimycin (KOS-953) administration, administration of any other chemotherapy,
biological, immunotherapy or investigational agent (therapeutic or diagnostic) within
14 days prior to receipt of study medication. Patients should be 6 weeks from last
dose of nitrosourea

- Severe dyspnea at rest caused by complications of advanced malignancy or requiring
supplementary oxygen therapy

- Congestive heart failure, or a left ventricular ejection fraction (LVEF) less than
50% assessed by multigated radionuclide angiography scan or echocardiography

- Any medical conditions that, in the Investigator's opinion, would impose excessive
risk to the patient

- Patients with previous malignancies unless free of recurrence for at least 5 years
except cured basal cell carcinoma of the skin, carcinoma-in-situ of either the
uterine cervix or urinary bladder, or Stage T1 or T2 prostate cancer whose PSA is < 2
ng/mL