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SOL in bladder (space-occupying lesion) means a bladder growth. Most of the times, the bladder growth will be malignant. So, your father needs early evaluation and treatment for his bladder growth. Based on CT scan and bladder biopsy, further treatment can be decided. For small and simple growths, endoscopic removal is possible.
For growths which extend into the bladder wall, surgery to remove bladder or radiotherapy is needed. For growths already spread beyond the bladder, chemotherapy may be needed. No point in delaying the treatment. Also, there is no need to panic. Consult a urologist in person who deals with urological cancers and get your father evaluated.
For further information consult a urologist online --> https://www.icliniq.com/ask-a-doctor-online/urologist