Inclusion Criteria:

          -  Subjects must have solid tumors with malignant lesions in the thorax, abdominal
             cavity, head and neck region, or extremities (any histology) likely to benefit from
             palliative radiotherapy; subjects requiring palliative RT for lesions in the spine or
             lesions adjacent to the spinal cord are excluded from this study

          -  Eastern Cooperative Oncology Group performance status (ECOG PS) =< 2

          -  Life expectancy >= 3 months

          -  Adequate hematologic, hepatic, and renal function

          -  Agree to use highly effective contraception (that is, methods with a failure rate of
             less than 1 percent per year) if the subject is male or a female of childbearing
             potential (female partners of childbearing potential of male subjects must also agree
             to use highly effective contraception)

          -  Other protocol defined inclusion criteria could apply

        Exclusion Criteria:

          -  Use of other anticancer therapy within 15 days before the first dose of M3541
             administration and should not be within the "at risk follow-up period" for that
             specific anticancer therapy. The use of any investigational agent is not allowed
             within 28 days before the first dose of M3541

          -  Residual toxicity due to previous anticancer therapy with no return to baseline or =<
             Grade 1 (except alopecia) according to CTCAE V4.03

          -  Extensive prior RT on more than 30 percent of bone marrow reserves (by Investigator
             judgment), or prior bone marrow/stem cell transplantation within 5 years before study
             start

          -  Prior RT to the same region that would be irradiated in this study

          -  Subjects at increased risk for radiation toxicities, such as known collagen vascular
             disease (example, scleroderma, Sjogren's disease, etc) or other inherited radiation
             hypersensitivity syndromes (example, Gorlin syndrome, Fanconi anemia,
             ataxia-telangiectasia, etc.)

          -  Surgical intervention within 28 days prior to the first dose of M3541 administration

          -  Known central nervous system metastases causing clinical symptoms or metastases that
             require therapeutic intervention. Subjects with a history of treated central nervous
             system (CNS) metastases (by surgery or radiation therapy) are not eligible unless they
             have fully recovered from treatment, demonstrated no progression for at least 2
             months, and do not require continued steroid therapy. Subjects with CNS metastases
             incidentally detected during Screening that do not cause clinical symptoms and for
             which standard of care suggests no therapeutic intervention is indicated, should be
             discussed with the Sponsor Medical Responsible

          -  Active difficulty swallowing, malabsorption or other chronic gastrointestinal disease
             or conditions (including pancreas deficiency requiring Creon therapy) that may hamper
             compliance and/or absorption of M3541

          -  Subjects currently receiving or unable to stop using medications or herbal supplements
             known to be potent inhibitors of cytochrome P450 (CYP) 3A and / or P-glycoprotein
             (P-gp) (CYP and / P-gp must stop at least 1 week before treatment with M3541) or
             potent inducers of CYP3A or P-gp (must stop at least 3 weeks before treatment with
             M3541) or drugs mainly metabolized by CYP3A with a narrow therapeutic index (must stop
             at least 1 day prior).

          -  Other protocol defined exclusion criteria could apply