In July 2000, from the Nephrology Department where he was being studied for chronic renal insufficiency secondary to nephroangiosclerosis, a 77-year-old man was referred to us due to the ultrasound finding of a 6 cm renal mass affecting the left kidney.
His personal history included COPD, hypertension and duodenal ulcus with pyloric stenosis.
To complete the studies we performed an abdomino-pelvic CT scan, which was reported as an 'infiltrative lesion involving the upper 2/3 of the left kidney with involvement of the pericapsular space and poorly defined borders'. Analytically, the presence of a monoclonal gammopathy with IgM of 4640 g/l (38-231) kappa by immunofixation was very remarkable. Other tests: positive bence-Jones proteinuria, bone marrow aspirate with 12.5% atypia and bone series without lytic lesions.

With the first diagnosis of renal mass associated with IgM monoclonal gammopathy (without fulfilling the criteria for IgM myeloma), a radical left nephrectomy was performed in August 2000.
The anatomopathological result was primary renal non-hodking B lymphoma of the MALT type (mucosa-associated lymphoid tumour).
The patient had a good post-operative evolution and was discharged with outpatient controls. In December 2000 a first control was carried out, showing an IgM of 3430 g/l in a first analysis and 4340 g/l in a second, so it was decided by the Haematology Department to start treatment with Chlorambucil. A control CT scan was performed which was reported as 'thickening of the perirenal fascia with fat deflecting compatible with inflammatory lesions or similar'. As there was no total evidence of recurrence, it was decided to monitor the patient closely with analytical and radiological controls and to maintain treatment with Chlorambucil. In January 2002 a new CT scan was performed and no signs of recurrence were found.
Currently the patient continues to be asymptomatic, with stable IgM levels (last control 48 g/l) on treatment with Chlorambucil.