Radiation therapy (RT) for breast cancer uses high-energy beams, typically X-rays, to target and destroy cancer cells remaining in the breast or chest wall after surgery. This localized treatment is common in breast-conserving therapy and is also used after a mastectomy to reduce the risk of recurrence. The radiation works by damaging the cancer cells’ DNA, preventing growth and division, a process that also affects healthy cells within the treatment field. Understanding the range of side effects is important for navigating treatment.
Localized Skin and Tissue Reactions
The most common side effects of breast radiation occur directly on the skin within the treated area, known as acute radiation dermatitis. These changes resemble a severe sunburn, typically manifesting as faint redness (erythema) around two to three weeks into the daily treatment schedule. The reaction intensifies as the cumulative radiation dose increases.
As treatment progresses, the skin may become dry, itchy, and tender, often accompanied by flaking or peeling (dry desquamation). This results from radiation damaging the basal layer of skin cells, impairing regeneration and barrier function. Areas where the skin naturally folds and rubs, such as the armpit or the crease beneath the breast, are often the most severely affected.
With higher doses, patients may develop moist desquamation, involving the skin breaking down, forming blisters, and weeping fluid. This breakdown is painful and increases the risk of localized infection, often peaking one to two weeks after the final treatment. Although most pronounced during this peak, the reaction generally begins to heal and resolve completely within a few weeks following treatment completion.
Beyond the skin, the breast tissue may temporarily experience swelling, tenderness, and heaviness during the treatment period. This temporary edema is a localized inflammatory response to the radiation exposure. These acute tissue changes generally subside within a few weeks to months after treatment concludes, though some persistent firmness may remain.
Systemic Symptoms During Treatment
While breast radiation is a localized treatment, patients frequently experience systemic side effects, primarily profound fatigue. Radiation-induced fatigue is a unique exhaustion not proportional to activity levels and often not relieved by rest. This symptom is believed to be caused by the body expending energy on repairing radiation-induced damage to healthy cells, alongside the inflammatory response.
Fatigue levels typically increase gradually throughout the treatment course, often peaking toward the final week of sessions. This exhaustion can significantly interfere with daily activities and quality of life. The fatigue usually begins to resolve within a few weeks after treatment completion, though the timeline for full recovery varies widely.
Other systemic symptoms are less common with breast radiation than with chemotherapy, but some patients report mild, transient discomfort. A slight increase in general body aches or a low-grade feeling of being unwell can occur as the body manages the physical stress of daily treatments. Rarely, some individuals may experience mild nausea or loss of appetite, particularly toward the end of treatment.
Delayed and Permanent Physical Changes
Months or years after breast radiation therapy, the treated area may show delayed and permanent physical alterations to the skin and underlying tissue. A common late effect is fibrosis, the formation of hardened scar tissue within the breast. This can lead to permanent firmness, shrinking, or distortion of the breast shape, sometimes making the treated breast smaller and denser than the untreated breast.
The skin surface can also undergo permanent changes, including the development of telangiectasias (small, visible, thread-like blood vessels). These tiny, dilated capillaries appear as fine red lines beneath the skin, resulting from long-term damage to small blood vessels in the radiated field. While harmless, these changes can alter the cosmetic appearance of the treated area.
If the radiation field included the lymph nodes, there is a delayed risk of developing lymphedema, a chronic swelling of the arm, hand, or breast. This condition is caused by damage to the lymphatic drainage system, leading to a buildup of protein-rich fluid in the tissues. Although the risk is lower with modern techniques, lymphedema can develop months to years after treatment and requires long-term management.
Rarely, radiation exposure can affect organs adjacent to the breast, such as the heart and lungs. Radiation pneumonitis, an inflammation of the lung tissue, is an uncommon side effect typically occurring one to three months post-treatment, presenting with a dry cough and shortness of breath. For women treated on the left side, there is a small, long-term risk of cardiac effects. However, modern techniques like Deep Inspiration Breath Hold (DIBH) are used to move the heart away from the radiation beam, significantly minimizing this risk.
Management and Supportive Care
Proactive skin care is important for managing localized reactions during and immediately after breast radiation. Patients should cleanse the treated area gently using only lukewarm water and a mild, non-fragranced soap, avoiding harsh scrubbing. Moisturizing the skin several times a day is recommended, using only unscented, alcohol-free lotions or creams approved by the care team to maintain hydration and soothe irritation.
Clothing choices can help mitigate discomfort; recommendations focus on wearing loose-fitting, soft cotton tops and avoiding restrictive underwire bras that may rub sensitive skin. The treated area must be protected from sun exposure, as ultraviolet light can intensify the skin reaction and cause long-term damage. Broad-spectrum sunscreen use is required even after the acute reaction subsides.
Managing radiation-induced fatigue involves energy conservation and light physical activity. Patients are encouraged to prioritize tasks and delegate responsibilities to conserve energy for necessary activities. Engaging in light-to-moderate exercise, such as walking for 30 minutes several times a week, is an effective strategy for combating cancer-related fatigue.
Patients should maintain open communication with their oncology team and report any new or worsening symptoms immediately. Signs that warrant prompt medical attention include a fever of 100.4°F or higher, persistent shortness of breath, a new or worsening dry cough, or signs of infection in the radiated skin (increased warmth, pain, or pus). Regular follow-up appointments allow the care team to monitor for acute and delayed side effects, ensuring appropriate supportive care.