Inclusion Criteria:

          -  Consenting adults of Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or
             1

          -  Histologically confirmed locally advanced or metastatic disease which has progressed
             during or after, failed to respond to, or for which there is poor tolerability or
             after a contraindication to available Standard of Care (SoC) treatment options as per
             the assessment of the investigator; initially, subjects with the disease below may be
             considered:

               1. Subjects who had Extensive Disease (ED-SCLC) at presentation who have progressed
                  on or after one line standard chemotherapy. If a subject had Limited Disease
                  (LD-SCLC) at presentation and received surgery and/or radiotherapy as first line
                  treatment (with or without chemotherapy) and has localized relapse, further local
                  treatment (such as surgery) should be considered in addition to the chemotherapy
                  options; For subjects with either ED-SCLC or LD-SCLC, if subjects relapse more
                  than 6 months after first-line treatment, re-treatment with their initial regimen
                  is recommended. Subjects may have received prior immunotherapy.

               2. Subjects with Human Epidermal Growth Factor Receptor (HR+)/(HER2-) metastatic BC
                  after a failure of prior SoC-treatments and who have received, if indicated, at
                  least one line of hormonal therapy, Cyclin-dependent kinase (CDK4/6) inhibitor
                  and/or everolimus for advanced or metastatic disease and at least one line of
                  chemotherapy for metastatic disease; subjects with a Breast Cancer (BRCA)-mutated
                  metastatic disease who may have received a Poly adenosine diphosphate ribose
                  polymerase (PARP) inhibitor, if available, are eligible; prior adjuvant hormonal
                  treatment and prior adjuvant chemotherapy are allowed.

          -  Documented progressive disease (radiological, based on RECIST v1.1) within 3 months
             prior to first study drug administration. Screening study-related images should be
             sent to the Imaging core laboratory (ICL).

          -  Adequate organ function determined within 28 days prior to 177Lu-OPS201
             administration, defined as follows:

               -  Haematological: white blood cells (WBC) ≥3000/μL, with absolute neutrophil count
                  ≥1000/μL, platelet ≥100,000/μL and haemoglobin ≥9 g/dL (without a need for
                  hematopoietic growth factor or transfusion support).

               -  Renal: Estimated glomerular filtration rate (eGFR) ≥55 mL/minute/1.73m2

               -  Hepatic: total serum bilirubin ≤2×ULN; aspartate aminotransferase/ alanine
                  aminotransferase ≤2.5×ULN (≤5×ULN if a subject has liver metastases)

          -  Formalin fixed paraffin embedded tumour sample (archival tumour sample obtained within
             1 month prior to concent from the primary or metastatic lesion OR is willing to
             undergo newly obtained biopsy prior to the first dose of study treatment. Subjects who
             are unable or do not concent to provide acceptable tissue may not be enrolled unless
             there has been prior agreement with the sponsor.

          -  68Ga OPS202 uptake in the target tissue (a primary tumour, lymph nodes longest
             diameter on PET/CT as confirmed by a central reader.

          -  Radiologically, ≥50% matching between the lesions detected on 68Ga OPS202-PET/CT and
             on 18F-fluorodeoxyglucose (18F-FDG)-PET/CT as confirmed by central reader

        Exclusion Criteria:

          -  Male subjects with BC.

          -  Unstable central nervous system metastasis

          -  Centrally located lung tumours that show radiogical evidence (CT or MRI) of either:

               -  cavitation or necrosis, or

               -  focal invasion for major blood vessels.

          -  Subjects had received chemotherapy within the previous 4 weeks or had not recovered
             from adverse events due to chemotherapy. Additional exclusion criteria were previous
             hemibody external radiotherapy, systemic radiotherapy with radioisotopes within the
             previous 24 weeks

          -  Previous chemotherapy within a cycle interval, curative radiotherapy within 4 weeks or
             palliative radiotherapy within 7 days prior to Investigational radiopharmaceutical
             product (IRPP) administration.

          -  Prior treatment with any other investigational medicinal product (IMP) within five
             half-lives of the previous IMP or within 2 weeks, if the previous compound is a
             mechanism-based molecularly targeted agent whose half-life is not well characterized
             and toxicities have not resolved from Grade 2 or higher prior to IRPP administration.

          -  Any unresolved NCI-CTCAE Grade 2 or higher toxicity (except alopecia and Grade 2
             platinum-therapy related neuropathy) from previous antitumour treatment and/or
             medical/surgical procedures/interventions.

          -  Nephrectomy, renal transplant or concomitant nephrotoxic therapy putting the subject
             at high risk of renal toxicity during the study as assessed by the investigator.

          -  Any significant medical or surgical condition that would affect safety or the
             assessment of efficacy or the ability of a person to comply with the protocol.

          -  Any condition that precludes the proper performance of PET and/or SPECT scans, CT
             scans and/or MRI:

               1. subjects who are not able to tolerate the CT contrast agent.

               2. subjects with metal implants or joint prosthesis (depending on the location, if
                  interferes with the PET and/or CT analysis)

               3. or any other objects that might interfere with the PET and/or CT analysis.

               4. subjects unable to raise arms for prolonged imaging purposes.

               5. subjects unable to lie still for the entire imaging time.

               6. subjects weighing greater than 130 kg (287 lb).

          -  Pregnant or lactating female. Female subject of childbearing potential who is
             unwilling to use acceptable method(s) of effective contraception during study
             treatment and through 6 months after the last dose of 177Lu-OPS201.

          -  Male subject who is unwilling to use acceptable method of effective contraception
             during treatment and through 6 months after the last dose of 177Lu-OPS201.