A single center, open-label, phase IIa, single arm, window of opportunity trial with IO103 and Montanide adjuvant in patients with surgically resectable BCC.

10 patients with BCC will be vaccinated with a peptide derived from the immune checkpoint molecule PD-L1. Patients will be vaccinated once every 2 weeks (Q2W) for 10 weeks and then evaluated for a clinical response.

Patients with clinical response to vaccination will continue with one vaccination once every 4 weeks (Q4W) for 12 weeks and thus receive 9 vaccinations in total over the course of 22 weeks.

Patients with no effect of treatment after 6 vaccinations will be treated with standard of care (SOC).

Inclusion Criteria:

1. Age ≥ 18

2. At least 1 histological verified superficial or nodular basal cell carcinoma on the body or limbs of bigger than 14 mm in the longest diameter

3. Willing to provide three 4 mm biopsies from the lesion/lesions

4. Not previously treated with a hedgehog pathway inhibitor

5. For women of childbearing potential: Agreement to use contraceptive methods with a failure rate of < 1 % per year during the treatment period and for at least 150 days after the treatment. Safe contraceptive methods for women are birth control pills, intrauterine device, contraceptive injection, contraceptive implant, contraceptive patch or contraceptive vaginal ring.

6. For men: Agreement to use contraceptive measures and agreement to refrain from donating sperm

7. The participant (or legally acceptable representative if applicable) provides written informed consent for the trial in accordance with ICH-GCP and local legislation prior to admission to the trial

8. Sufficient bone marrow function, i.e.

   1. Leucocytes ≥ 1,5 x 109
   2. Granulocytes ≥ 1,0 x 109
   3. Thrombocytes ≥ 20 x 109

2. Creatinine < 2.5 upper normal limit, i.e. < 300 μmol/l 3. Sufficient liver function, i.e.

1. ALAT < 2.5 upper normal limit, i.e. ALAT <112 U/l
2. Bilirubin < 30 U/l

Exclusion Criteria:

1. The patient has a history of life-threatening or severe immune related adverse events on treatment with another immunotherapy and is considered to be at risk of not recovering
2. The patient has a history of severe clinical autoimmune disease
3. The patient has a history of pneumonitis, organ transplant, human immunodeficiency virus positive, active hepatitis B or hepatitis C
4. The patient has any condition that will interfere with patient compliance or safety (including but not limited to psychiatric or substance abuse disorders)
5. The patient is pregnant or breastfeeding
6. The patient has an active infection requiring systemic therapy
7. The patient has received a live virus vaccine within 30 days of planned start of therapy
8. Known side effects to Montanide ISA-51
9. Significant medical disorder according to investigator; e.g. severe asthma or chronic obstructive lung disease, dysregulated heart disease or dysregulated diabetes mellitus
10. Concurrent treatment with other experimental drugs
11. Any active autoimmune diseases e.g. autoimmune neutropenia, thrombocytopenia or hemolytic anemia, systemic lupus erythematosus, scleroderma, myasthenia gravis, autoimmune glomerulonephritis, autoimmune adrenal deficiency, autoimmune thyroiditis etc.
12. Severe allergy or anaphylactic reactions earlier in life.