A Study of the Intratumoral Microdose Administration of PBA-0405 in Patients With Solid Tumors

Inclusion Criteria:

1. Ability and willingness to comply with the study's visit and assessment schedule.

2. Male or female ≥ 18 years of age at Visit 1 (Screening).

3. Pathologic diagnosis of HNSCC, STS (see restrictions in Note below), or TNBC (seerestrictions in Note below; TNBC defined as estrogen receptor negative [<1% positivetumor cells], progesterone receptor negative [<1% positive tumor cells], and humanepidermal growth factor receptor 2 negative [0 to 1+]) with a tumor planned forsurgical resection. Note: For STS, only the following subtypes are eligible: undifferentiatedpleomorphic sarcoma, alveolar soft part sarcoma, synovial sarcoma, cutaneousangiosarcoma, or myxofibrosarcoma. Note: For TNBC, if prior neoadjuvant therapy, evidence of progressive disease, atthe discretion of the investigator.

4. Ability and willingness to provide written informed consent. Voluntary writtenconsent must be given before performance of any study related procedure not part ofstandard medical care, with the understanding that consent may be withdrawn by thepatient at any time without prejudice to future medical care.

5. As assessed or confirmed by the surgeon, at least one lesion (primary tumor,recurrent tumor, metastatic tumor, or metastatic lymph node) that is surfaceaccessible for CIVO injection that contains viable minimum tumor tissue volume andcharacteristics (e.g., based on clinical evaluation, available pre-operativeimaging, pre-injection ultrasound imaging, or pathology reports indicating lesionwith appropriate viable tumor volume without excessive cysts or necrosis) and forwhich there is a planned surgical intervention. The patient's presentation, surgicaland pathology plan may determine whether a lesion is eligible with respect to agiven CIVO MID needle configuration.

6. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.

7. Female patients who:

• Are postmenopausal for at least one year before the screening visit, OR

• Are surgically sterile, OR

• Are of childbearing potential who agree to practice a highly effective methodof contraception from the time of signing the ICF up to 3 months following theend of study participation OR agree to completely abstain from heterosexualintercourse.

• Agree to refrain from donating ova during study participation.

Male patients, even if surgically sterile (i.e., status post-vasectomy), who:

• Agree to practice effective barrier contraception from the time of signing the ICFup to 3 months following the end of study participation OR agree to completelyabstain from heterosexual intercourse.

• Agree to refrain from donating sperm during study participation.

Exclusion Criteria:

1. Tumors near or involving critical structures for which, in the opinion of thetreating clinician, injection would pose undue risk to the patient.

2. Female patients who are:

• Both lactating and breastfeeding, OR

• Have a positive β-subunit human chorionic gonadotropin (β-hCG) pregnancy testat screening verified by the Investigator.

3. Any uncontrolled intercurrent illness, condition, serious medical or psychiatricillness, or circumstance that, in the opinion of the Investigator, could interferewith adherence to the study's procedures or requirements, or otherwise compromisethe study's objectives.

4. HNSCC known to be of cutaneous origin.

5. Patients with uncontrolled autoimmune diseases (see Appendix 1 for examples)requiring systemic treatment

6. Patients with known HIV/AIDS.

7. Patients with known uncontrolled active hepatitis B (defined as hepatitis B surfaceantigen [HBsAg] positive or detectable hepatitis B virus [HBV] DNA) or hepatitis C (defined as anti-hepatitis C virus antibody [anti-HCV Ab] positive and detectablehepatitis C virus [HCV] RNA) infection. Note: Hepatitis B and C screening tests are not required unless:

• Patient has a known history of hepatitis B/C infection

• Mandated by local health authority

8. Use of any of the following ≤ 3 weeks prior to CIVO injection:

9. Systemic anti-cancer therapy (e.g., cytotoxic chemotherapy, targeted agents, orcheckpoint inhibitor immunotherapy, etc.),

10. Immunosuppressive drugs (e.g., calcineurin inhibitors)

11. Biological response modifiers for autoimmune disease

12. Systemic glucocorticoids: oral or parenteral corticosteroids at a dose ≥ 20mg/day prednisone, or equivalent Note: physiologic replacement dosing ofsteroids (≤ 3 mg/m2/d prednisone or equivalent), low-dose corticosteroids fordye allergies prior to staging scans or use in anti-emetic prophylaxis forpatients undergoing chemotherapy, or topical steroids, are allowed

13. Hematopoietic growth factors

14. Chemotherapy

15. Local radiotherapy of the target lesion planned for CIVO injection and surgicalresection

16. Patients who have received a live or live attenuated vaccine within 4 weeks of thebaseline/screening visit.

17. Patients who have had allogenic tissue/solid organ transplant

18. Patients with an active infection requiring systemic therapy.

19. Patients for whom participation on this study results in a delay of planned surgicalintervention.