A Study of KM257 in Patients With Advanced HER2-positive or Expressing Solid Tumors.

Inclusion Criteria:

1. Able to understand, voluntarily participate and willing to sign the ICF.
2. Male or female subject >= 18 years and =<75 years.
3. Histologically or cytologically confirmed advanced solid tumors.
4. HER2 positive or expressing.
5. ECOG score 0 or 1.
6. According to the definition of RECIST1.1, for Part1a, the patient has evaluable butNon-measurable lesion can be accepted. For Part1b, the patient has at least onemeasurable lesion.
7. Life expectancy≥12weeks.
8. Adequate organ function.
9. Subjects (women of child-bearing potential and males with fertile female partner) mustbe willing to use viable contraception method.

Exclusion Criteria:

1. primary CNS tumors (including meningeal tumors), symptomatic or untreated CNSmetastases(including meningeal metastases).
2. Subjects who had other malignancies in the 2 years prior to the first administrationof the investigational drug were excluded in Phase Ib, except those who had basal cellcarcinoma, breast cancer in situ, or cervical cancer in situ and had no recurrence andmetastasis after radical therapy.
3. Accepted any other anti-tumor drug therapies within 2 weeks before first dose.
4. Accepted major surgery or radical radiotherapy within 4 weeks before first dose;Accepted palliative radiotherapy within 2 weeks before first dose; Acceptedradioactive agents(strontium, samarium, etc.)for therapeutic purposes within 8 weeksbefore first dose.
5. Participating in other studies involving investigational drug(s) ≤ 4 weeks before thefirst dose of KM257.
6. Subjects with interstitial lung disease or non-infectious pneumonia and relatedhistory.
7. Infection with HIV disease.
8. Active hepatitis.
9. Had an active infection requiring systemic treatment within 2 weeks prior to initialadministration of the investigational drug.
10. Cavity effusion (pleural effusion, ascites, pericardial effusion, etc.) are not wellcontrolled. Subjects are eligible with clinically controlled and stable neurologic function >= 4weeks, which is no evidence of CNS disease progression; Subjects with
11. Subjects who have received organ transplants.
12. Unresolved toxicities ( Common Terminology Criteria for Adverse Event (CTCAE, version 5), grade greater than or equal to2) from prior anti-cancer therapy. (with theexception of alopecia, the special provisions of inclusion criteria);
13. Subjects who have a history of severe allergic reactions to antibody medications orhave a history of severe allergic asthma (CTCAE V5.0 grade ≥3).
14. Subjects with a known history of alcohol or drug abuse.
15. History of myocardial infarction or unstable angina within 6 months prior toenrollment, congestive heart failure (NYHA Class≥2), or clinically significant cardiacdisease，LVEF<50%，QTc Fridericia (QTcF) > 470 ms for female, QTc Fridericia (QTcF) > 450 ms for male.
16. History of TIA or stroke within 6 months prior to initial administration of KM257.
17. Subjects known to have a mental illness that may affect trial compliance.
18. The investigator considers that the subject has any clinical or laboratoryabnormalities or other reasons that would disqualify him or her from participating inthis clinical study.
19. Part1b cohort 2: subjects with known mutations in exons 2, 3, and 4 of KRAS/NRAS andin V600E of BRAF.