According to data published in 2021 breast cancer is the most commonly diagnosed tumor worldwide surpassing lung cancer. [1]

In recent years, this has led research to focus on developing therapies with minimal impact on patient’s lives.

In this context, ablation has emerged as a promising procedure. Ablation involves the local application of extreme temperatures—cold in the case of cryoablation, or heat in the case of radiofrequency and microwaves—or the application of electrical pulses in the case of electroporation (Fig. 1). The goal of these procedures is to achieve, as a minimally invasive procedure, an irreversible destruction of tumor cells through cellular apoptosis (natural cell death) or coagulative necrosis (inflammation and coagulation). [2]

The most commonly used ablative techniques are radiofrequency and microwaves. Both are heating processes based on electromagnetic fields. They differ in wavelength: microwaves are a band of low frequencies (300 MHz – 3 GHz) within the radiofrequency spectrum (3 KHz – 300 GHz). (Fig. 2). [3]

Pathophysiology

Microwave thermal ablation is an ultrasound-guided technique that causes irreversible damage to solid tumor cells through a complex cascade of numerous pathophysiological events, which are essential to understand for interpreting radiological imaging. [4]

Microwaves not only induce tissue necrosis through thermoablation but also trigger a local inflammatory response that activates the immune system. The inflammation of the entire necrotic tissue ultimately transforms the entire ablated area into fibrosis, resulting in a reduction in lesion size. [5]

Additionally, during ablation, the thermal energy also destroys the blood vessels surrounding the tumor cutting off its blood supply and reducing the possibility of tumor metastasis. [6]

Indications

Microwave treatment is indicated for patients who cannot undergo surgery due to high surgical risk (ASA III-IV) or other surgical contraindications. It is performed on tumors confirmed by pathological anatomy, which are solitary, round/oval in shape, smaller than 3 cm, and without intraductal extension. These criteria may be reconsidered for larger tumors or those with elongated or irregular shapes (Fig. 3). [7]

Thermoablation can also be considered for histologically confirmed benign tumors to avoid invasive surgeries. For fibroadenomas it is proposed when they increase in size or cause anxiety or local symptoms in patients.

In the case of benign tumors with a risk of malignancy microwave therapy is not indicated because they require clear surgical margins (Phyllodes tumors). [8]

Step by step in our experience

Before performing the procedure, the mass must first be evaluated using various imaging techniques including, if possible, a functional study (MRI, contrast-enhanced mammography). This assessment helps determine the size of the lesion, its location, depth, and proximity to the skin or pectoral fascia.

The treatment begins with the application of local subcutaneous anesthesia. Next, the antenna with an active tip that generates microwaves is inserted into the lesion increasing the local temperature (Fig. 4).

To determine the amount of heat to apply and the duration of the procedure, we use reference tables. Based on the two maximum tumor diameters, these tables indicate the required power (Watts, W) and the procedure's duration. (Fig. 5).

When the needle starts to operate and generates heat, an artifact is formed causing a shadow that prevents visualization of the needle tip and the lesion. (Fig. 6).

A complete ablation is considered when the ablation is performed with a safety margin of at least 5 mm around the edges of the lesion. For this, it is important to consider the tumor's location, proper antenna positioning, the power (Watts), and the established duration.

When the tumor is located less than 1cm from the skin, hydrodissection is used to separate the tumor from the subcutaneous tissue. This technique involves the continuous infusion of saline solution into the dermis. Hydrodissection is also indicated if the tumor is close to the pectoral fascia. In this case, the saline infusion would be performed adjacent to the deep margin of the tumor.

Complications

The complications of the procedure are generally mild. The most common are pain and inflammation. Many patients report a perceived increase in tumor volume during the first three months, which can be explained by inflammation and fat necrosis.

On the other hand, the risk of local burns can be minimized with proper hydrodissection or by using lower power levels and a longer ablation time. [7]

Follow-up

Several follow-up assessments are recommended after the procedure (Fig. 7). [9]

- 1 month post-ablation → ultrasound and mammography.

- 3 months post-ablation → ultrasound only.

- 6 months post-ablation → functional study.

- 1 year post-ablation → mammography, ultrasound, and functional study.

- 2 years post-ablation →mammography and functional study.

We must consider that at the one-month follow-up, it may appear that the tumor has increased in size, which can be explained by the inflammatory changes induced by thermoablation.

It is at the 6-month follow-up when we assess, through a functional study, the viability of the tumor and the need for a new ablation session.