A Study of KK2269 in Adult Participants With Solid Tumors

* Key Common Inclusion Criteria for Parts 1 and 2:

  * Patients who are ≥ 18 years old at the time of informed consent
  * Patients who have disease measurable by RECIST v1.1
  * Patients with an ECOG PS of 0 or 1
  * Patients with a life expectancy of at least 3 months in the judgement of the investigator or subinvestigator
  * The specified periods have passed respectively after the completion of previous cancer treatments as of the date of enrollment at the time of the first dose of KK2269
  * Patients who agree to use a medically effective method of contraception
* Key Additional Inclusion Criterion for Part 1:

  •Patients with histological or cytological evidence of at least one locally advanced or metastatic non-CNS solid tumor
* Key Additional Inclusion Criteria for Part 2:

  •Patients with histological or cytological evidence of any of the following disease: Gastric adenocarcinoma, GEJ adenocarcinoma, or esophageal adenocarcinoma, NSCLC (Only patients with NSCLC will be enrolled in the expansion part)

  •Patients who are suitable for docetaxel treatment
* Key Common Exclusion Criteria for Parts 1 and 2:

  * Patients with an uncontrolled or serious intercurrent illness
  * Patients with known active central nervous system metastasis
  * Patients with a history of ≥ Grade 3 allergic reaction to any antibody drug
  * Patients with a history of autoimmune disease
  * Patients with a history of HIV, HBV, or HCV at screening
  * Patients who have a history of primary immunodeficiency
* Key Additional Exclusion Criterion For Part 2:

  * Patients with a history of treatment with docetaxel