Study of RYZ401 in Subjects With Solid Tumors Expressing SSTRs.

Inclusion criteria:

* At least 18 years old at the time of signing the main study informed consent form (ICF).
* Histologically confirmed:

Dose Escalation (all cohorts): Grades 1-3 WD, metastatic or locally advanced and unresectable NET at any primary site, including, but not limited to, GI, pancreatic, lung, thyroid, breast, urogenital, and adrenal tumors.

* Dose Expansion Cohort A: Grades 1-3 WD, metastatic or locally advanced and unresectable GEP-NETs
* Dose Expansion Cohort B: metastatic or locally advanced and unresectable tumors known to frequently express SSTR, limited to the following indications:

  * WD NETs (Grades 1-3) from primary sites other than gastrointestinal and pancreatic (including, but not limited to, lung, thyroid, breast, urogenital, and adrenal tumors) Meningioma (Grades 1-3)

    * SSTR-positive disease, as assessed by SSTR-PET imaging
    * Adequate renal, hematologic and hepatic function

Exclusion criteria:

* Prior RPT, including Lu-177.
* Prior solid organ or bone marrow transplantation.
* Use of chronic systemic steroid therapy.
* Significant cardiovascular disease
* Resistant hypertension
* Uncontrolled diabetes
* Prior history of liver cirrhosis
* HIV, hepatitis B infection or known active hepatitis C virus infection.

Note: Additional criteria may apply and will be assessed by the study site