This is a phase 1 study to evaluate safety and tolerability of Telomelysin (OBP-301) in combination with radiation therapy in patient with esophageal cancer who are not applicable to standard therapy.

After screening, patients will undergo a combination therapy of OBP-301 with radiation therapy for 6 weeks. At Day 1, Day 18 and Day 32, OBP-301 is directly injected to the location of the lesion. From Day 4, patients receive radiation therapy. Patients will be automatically entered follow-up period for 12 weeks to be observed tolerance and safety.

This study is designated as standard 3 + 3 dose escalation study. The first 3 patients will be evaluated with low-dose of OBP-301 and then the study move onto the high-dose cohort of OBP-301. When the DLT (Dose Limiting Toxicity) is observed, 3 more patients will be enrolled in the dose level.

Key Inclusion Criteria:

1. Patients who have primary tumor or metastatic lesion of histologically or cytologically diagnosed with esophageal carcinoma.
2. Patients are feasible for injection of OBP-301 into target legion
3. Patients aged in 20 to 89 years.
4. Patients with ECOG Performance Status Score ≤ 2.
5. Patient who have life expectancy longer than 12 weeks.
6. Patients who are not applicable to standard therapy.
7. Patients who have adequate organ function.

Key Exclusion Criteria:

1. Patients who have an active, treatment-required concomitant malignancy.
2. Patients who had been enrolled within 4 weeks to other clinical trials of unapproved drugs.
3. Patients who have had chemotherapy within 4 weeks.
4. Patients who have treatment history of cancer immunotherapy.
5. Patients who had radiotherapy to treatment targeted lesion.
6. Patients who have active infection which required systemic treatment.
7. Patients who are scored III or IV by NYHA (New York Heart Association).
8. Patients who are judged as inappropriate to this trial by investigator(s).