Everolimus, Letrozole and Trastuzumab in HR- and HER2/Neu-positive Patients

Inclusion Criteria: * Signed informed consent obtained prior to any screening procedures * Performance status =\< 1 * Absolute neutrophil count (ANC) \>= 1 x 10\^9/L * Platelets \>= 75 x 10\^9/L * Hemoglobin (Hb) \> 8 g/dL * Total serum bilirubin =\< 2.0 mg/dL * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =\< 2.5 x upper limit of normal (ULN) (=\< 5 x ULN in patients with liver metastases) * International normalized ratio (INR) =\< 2 * Serum creatinine =\< 1.5 x ULN * Fasting serum cholesterol =\< 300 mg/dL or =\< 7.75 mmol/L and fasting triglycerides =\< 2.5 x ULN; Note: in case one or both of these thresholds are exceeded, the patient can only be included after initiation of appropriate lipid lowering medication * Histologically confirmed advanced solid tumors with HR-positivity defined as \> 1% on immunohistochemistry (estrogen receptor-positive with or without positivity for the progesterone receptor) and HER2/neu positivity (3+ on IHC and/or 2+ on IHC and FISH amplified, or by v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2 \[ERBB2\] mutation on next generation sequencing) * Must have measurable or evaluable disease * At least 4 weeks since the last dose of chemotherapy, immunotherapy, surgery, or radiation therapy (exception: patients may have received palliative low dose radiation therapy one week before treatment provided it is not given to the only targeted lesions); at least 6 weeks for therapy which is known to have delayed …