Inclusion Criteria:

          -  Subject has histologically or cytologically confirmed metastatic or locally advanced,
             unresectable solid tumors harboring EGFR mutations.

          -  Subject has Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1.

          -  Subject must meet all of the following criteria on the laboratory tests that will be
             performed within 7 days prior to enrollment. In case of multiple laboratory data
             within this period, the most recent data should be used.

               -  Neutrophil count ≥ 1,000/mm3

               -  Platelet count ≥ 7.5 × 104/mm3

               -  Hemoglobin ≥ 9.0 g/dL

               -  Lymphocyte count ≥ 500/mm3

               -  Estimated glomerular filtration rate (eGFR) of > 50 ml/min as calculated by the
                  Cockcroft-Gault Method

               -  Total bilirubin (TBL) < 1.5 × upper limit of normal (ULN; except for subjects
                  with documented Gilbert's syndrome)

               -  Aspartate aminotransferase (AST) and ALT < 3.0 × ULN

               -  Serum sodium level is ≥ 130 mmol/L

          -  Female subject must either be:

               -  Of nonchild bearing potential:

                    1. Postmenopausal (defined as at least 1 year without any menses) prior to
                       screening, or

                    2. Documented surgically sterile or status post hysterectomy (at least 1 month
                       prior to screening).

               -  Or, if of childbearing potential:

                    1. Agree not to try to become pregnant during the study and for 28 days after
                       the final study drug administration,

                    2. Must have a negative serum pregnancy test at screening and day -1, and

                    3. If heterosexually active must use two forms of birth control* (at least one
                       of which must be a barrier method) starting at screening and throughout the
                       study period and for 28 days after the final study drug administration.

          -  Female subject must not be breastfeeding at screening or during the study period, and
             for 28 days after the final study drug administration.

          -  Female subject must not donate ova starting at screening and throughout the study
             period, and for 28 days after the final study drug administration.

          -  Male subject and his female spouse/partner who is of childbearing potential must be
             using highly effective contraception consisting of two forms of birth control* (one of
             which must be a barrier method) starting at screening and continue throughout the
             study period and for 90 days after the final study drug administration.

          -  Male subject must not donate sperm starting at screening and throughout the study
             period and for 90 days after the final study drug administration.

             *Acceptable forms of birth control include:

          -  Established use of oral, injected or implanted hormonal methods of contraception.

          -  Placement of an intrauterine device (IUD) or intrauterine system (IUS).

          -  Barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault
             caps) with spermicidal foam/gel/film/cream/suppository.

        Exclusion Criteria:

          -  Subject has an ongoing toxicity ≥ Grade 2 (Common Terminology Criteria for Adverse
             Event [CTCAE] v4.03) attributable to prior medication to treat solid tumor (except
             alopecia) at the time of screening.

          -  Subject has known history of serious hypersensitivity reaction to ASP8273, or any
             component of the formulation used.

          -  Subject has received investigational therapy within 28 days or 5 half-lives, whichever
             is shorter, prior to the first dose of study drug.

          -  Subject has received a prior EGFR inhibitor within 6 days prior to the first dose of
             study drug.

          -  Subject has had any of the following within 14 days prior to the first dose of study
             drug:

               -  A treatment with any other agent with antitumor activity including chemotherapy,
                  radiotherapy, or immunotherapy

               -  A major surgical procedure (other than study related biopsy), or a major surgical
                  is planned to occur during the study

               -  Blood transfusions or hemopoietic factor therapy

               -  Evidence of active infection requiring systemic therapy

          -  Subject has symptomatic central nervous system (CNS) metastasis. Subject with
             previously treated brain or CNS metastases are eligible provided that the subject has
             recovered from any acute effects of radiotherapy and is not requiring steroids, and
             any whole brain radiation therapy was completed at least 2 weeks prior to study drug
             administration, or any stereotactic radiosurgery (SRS) was completed at least 1 week
             prior the first dose of study drug.

          -  Subject has ≥ CTCAE v4.03 Grade 2 neuropathy.

          -  Subject has a known history of a positive test for hepatitis B surface antigen (HBsAg)
             or hepatitis C antibody (anti-HCV).

          -  Subject has a known history of a positive test for human immunodeficiency virus (HIV)
             infection.

          -  Subject has history of drug-induced interstitial lung disease (ILD) or any evidence of
             active ILD.

          -  Subject has severe or uncontrolled systemic diseases including uncontrolled
             hypertension (blood pressure > 150/100 mmHg) or active bleeding diatheses.

          -  Subject has ongoing cardiac arrhythmia that is Grade ≥ 2 or uncontrolled atrial
             fibrillation of any grade.

          -  Subject currently has Class 3 or 4 New York Heart Association congestive heart
             failure.

          -  Subject has history of severe/unstable angina, myocardial infarction, or
             cerebrovascular accident within 6 months prior to the first dose of study drug.

          -  Subject has concurrent corneal disorder or any ophthalmologic condition which, in the
             Investigator's opinion, makes the subject unsuitable for study participation (e.g.,
             advanced cataracts, glaucoma, or subject is unable to undergo a comprehensive
             ophthalmologic exam).

          -  Subject has history of gastrointestinal ulcer or gastrointestinal bleeding within 3
             months prior to the first dose of study drug.

          -  Subject has difficulty taking oral medication or any digestive tract dysfunction or
             inflammatory bowel disease that would interfere with the intestinal absorption of
             drug.

          -  Subject who has received strong/moderate inhibitors or inducers of CYP3A4 within 14
             days prior to the first dose of study drug.