Detection of breast cancer at early stages is very important to eliminate the possibility of breast removal in women. The dielectric changes caused in the breast tissues due to the formation of cancerous cells can be monitored by a biocompatible implant. Therefore a novel flexible implantable antenna sensor with the dimension 5mm x 5mm x 0.25mm working at the ISM band (2.45 GHz) is proposed for proactive detection of cancer cells inside the human breast. It can be wirelessly powered up through Wireless Power Transfer (WPT) working at 1.2-1.4 GHz (mid-band). An ultra-miniature structure of the implantable antenna (12.5mm 3 ) is achieved by using closed loops and meandered strips making the implant an efficient radiator. A reflection coefficient of -17dB is achieved with a -10dB bandwidth of 330 MHz inside the abnormal breast tissue (ε r -52.7). Once the permittivity of the breast tissue increases and crosses 15, the radiator starts working and a maximum of -10dBi gain is achieved. The proposed antenna is fabricated and the simulated results are verified. It can be used for proactively detecting the cancer cells inside the human breast and treating it before it spreads to the nearby tissues. Patients with a genetic history of breast cancer can be administered the proposed implant for proactive monitoring of the development of cancerous cells.