Inclusion Criteria :

          -  Signed informed consent form prior to all study procedures

          -  Aged 18 years or older.

          -  Histologically or cytologically confirmed metastatic or locally advanced disease and
             no compelling treatment option as per standard-of-care and documented decision by a
             multidisciplinary oncology board including a specialist of the concerned pathology.

          -  Subjects have: (a) pancreatic ductal adenocarcinoma (PDAC), or (b) colorectal cancer
             (CRC), or (c) gastric adenocarcinoma (GC), or (d) gastrointestinal stromal tumours
             (GIST), or (e) squamous-cell carcinoma of head and neck (SCCHN), or (f) Ewing Sarcoma
             (ES)

          -  Tumour tissue expressing NTSR1 as determined by uptake of 177Lu-3BP-227 (screening
             formulation) in tumour lesions judged by the investigator to more avid than in the
             non-tumoral surrounding tissue based on whole body scan (planar scintigraphy); single
             photon emission computed tomography (SPECT)/ computed tomography (CT) can be performed
             as per investigator's judgement.

          -  Measurable disease (based on RECIST version1.1).

          -  Documentation of progressive disease in the 6 months prior to study start (treatment).

          -  Eastern Cooperative Oncology Group performance status of 0 or 1 (unless if disability
             is related to surgery in ES and Agreed with the Sponsor).

          -  Adequate organ function as evidenced by: (a) Leukocytes ≥3000/μL (b) Absolute
             neutrophil count ≥1500/µL (c) Platelets ≥75,000/µL (d) Hb >9 g/dL or >10 g/dL (if
             history of cardiac disease) (e) Total serum bilirubin ≤2 times upper normal
             institutional limits (ULN) (f) Aspartate aminotransferase/alanine aminotransferase
             (ALT) ≤2.5×ULN (or ≤5×ULN, if subject has liver metastases) (g) Estimated glomerular
             filtration rate (eGFR) ≥55 mL/min.

          -  Estimated life expectancy >3 months.

          -  Female subjects must not be pregnant or lactating at study entry and during the course
             of the study and must not become pregnant for at least 6 months following the last
             study treatment. Women of childbearing potential must agree to use a highly effective
             method of contraception. Because CT scanning is part of the long-term follow-up (every
             12 ±2 weeks), female subjects should not become pregnant until the end of study
             assessments.

          -  For male subjects, must not father children during the study and for at least 6 months
             after the last study treatment and in addition must agree to use a condom for this
             period to protect his partner from contamination with the IMP. For males with partners
             who are of child bearing potential, effective contraception is a combination of male
             condom with either cap, diaphragm or sponge with spermicide (double barrier methods),
             but these are not considered to be highly effective. A man is considered to be
             infertile if he has had bilateral orchidectomy or successful vasectomy. Effective
             contraception includes a female partner of childbearing potential if she is using
             highly efficacious contraception, but the male subject must agree to use a condom to
             protect his partner as described above.

          -  Must be willing and able to comply with study restrictions and to remain at the clinic
             for the required time during the study period and willing to return to the clinic for
             the follow-up evaluation, as specified in the protocol.

        Exclusion Criteria :

          -  Prior treatment received (a) Any antitumour treatment since last documentation of
             disease progression (b) Any chemotherapy within 3 weeks or nitrosourea within 6 weeks
             prior to first treatment investigational medicinal product (IMP) administration (c)
             Any curative radiotherapy within 4 weeks, or palliative radiotherapy within 7 days
             prior to first treatment IMP administration (d) Any monoclonal antibodies within 4
             weeks or tyrosine kinases inhibitors within 2 weeks prior to the first treatment IMP
             administration, (e) Any other IMP within 2 weeks prior to first treatment IMP
             administration, if the previous compound is a mechanism-based molecularly targeted
             agent whose half-life (t1/2) is not well-characterised.

          -  Brain metastases.

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

          -  Only non measurable metastatic bone lesions

          -  Existing or planned colostomy during study participation.

          -  Any history of inflammatory bowel disease.

          -  Any uncontrolled significant medical, psychiatric or surgical condition or laboratory
             finding, that would pose a risk to subject safety or interfere with study
             participation or interpretation of individual subject results.

          -  Clinically significant abnormalities on electrocardiogram (ECG) at screening including
             corrected QT interval (Fridericia's formula) >450 msec for males or 470 msec for
             females at screening.

          -  Previously received external beam irradiation to a field that includes more than 30%
             of the bone marrow or kidney.

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

          -  Known allergy to IMP or its excipients administered in this study, including imaging
             contrast media.

          -  Positive pregnancy test (female subjects).

          -  Likely to be uncompliant or uncooperative during the study, in the judgment of the
             investigator.

          -  Unable to understand the nature, scope and possible consequences of the study, in the
             judgment of the investigator.

          -  Sponsor employees or investigator site personnel directly affiliated with this study,
             and their immediate families. Immediate family is defined as a spouse, parent, child
             or sibling, whether biological or legally adopted.