Researchers in Germany have developed a microchip sensor that can be implanted close to a tumour to monitor its growth.
The device tracks oxygen levels in nearby tissue to detect if a tumour is expanding.
Results are then transmitted wirelessly to a patient's doctor - reducing the need for frequent hospital scans.
Future designs will include a medication pump that can deliver drugs directly to the affected area.
Researchers hope this will lead to less aggressive and more targeted cancer treatments.
Medical engineers at the Technical University in Munich developed the device as a way to track and treat tumours that are difficult to reach, or better left alone.
"There are some tumours which are hard to remove - for example, close to the spine. You run the risk of cutting the nerve if you remove them surgically. Or the problem may be that the tumour is growing slowly, but the patient is elderly," said project manager Sven Becker.
"In these cases it's better to monitor the tumour, and only treat it if there's a strong growth phase."Drug pump
The sensor is implanted next to a tumour, and measures the concentration of dissolved oxygen in nearby tissue fluid. If this drops it can indicate aggressive growth, and doctors can be alerted.
"The microelectronic chip has a set of electrodes that detect oxygen saturation. It transmits this sensor data to an external receiving unit that's like a small box you carry around in your pocket," explained Mr Becker.
"From there it goes into the doctor's PC - and they can look at the data and decide whether the tumour activity is getting worse."
Researchers believe this will reduce the need for frequent hospital check-ups.
"Normally you would have to go to the hospital to be monitored - using machines like MRI to detect the oxygen saturation. With our system you can do it on the go," said Mr Becker.
The team plans to add a medication pump to the chip that can release chemotherapeutic drugs close to a tumour if treatment is needed.
Mr Becker hopes this will prove more effective and less toxic for future cancer patients.
"In traditional chemotherapy you put drugs into the whole body - which can have awful side effects. We want to add a pump to our chip, so if the sensor detects growth, you can apply microscopic amounts directly to the tumour," he said.
"Patients can be treated more quickly and with less side effects, because it's local."
Development is still in its early stages, but researchers hope to have a device ready for medical use within ten years.