A method of diagnosis and treatment of malignant tumours by the steps locating an area containing of lymph systems including lymph nodes and lymph ducts draining the area around a tumour, injecting a magnetic particles containing marker compound in and around the tumour, the compound migrating into the lymph system and lymph nodes draining the area around said tumour; making images of such area, by methods such as X-ray, Ultrasound and the like and identifying locations of lymph nodes, conducting biopsies of lymph nodes responding to the marker compound to determine the tumour status of such lymph nodes, and operating to remove both the malignant tumour and tumour-invaded lymph nodes, and subsequently subjecting the area around said tumour and containing any remaining said lymph nodes and ducts to an hyperthermal treatment by an oscillating electromagnetic field thereby inducing heat in said magnetic particles containing marker compound, to break down any potentially remaining tumour cells in the said remained micro lymph nodes in that area. Also disclosed is a marker compound for the marking , detecting, and possible subsequent treatment of the lymph system draining the tumour area.