Radiation-Induced Sarcomas - Atypical Presentations on Imaging

Introduction

Radiation therapy (RT) plays a pivotal role in cancer management. They are used to target and kill cancerous cells. Despite its significance in cancer treatment, radiation therapy also comes with risks. It can have long-term consequences, and one of the uncommon but severe complications of radiation therapy is the occurrence of radiation-induced sarcomas. The overall incidence of radiation-induced sarcoma is lower than one percent for cancer patients treated with radiation therapy. However, timely diagnosis is essential for prompt management and favorable outcomes. This article explains the uncommon presentations of radiation-induced sarcoma on imaging that can cause complexities in diagnosing and treating these rare malignancies.

What Is Radiation-Induced Sarcoma?

Radiation-induced sarcoma (RIS) is a secondary cancer that originates in the irradiated bone or soft tissues after some period of high-dose radiotherapy. Radiation-induced sarcomas are usually high-grade tumors and have a poor prognosis compared to primary sarcomas. Osteosarcoma and undifferentiated pleomorphic sarcoma are the two most common histological types. The occurrence rate of radiation-induced sarcoma is very rare, about one percent at 10 years. Due to the rarity, there are no proper guidelines or randomized prospective clinical trials on radiation-induced sarcoma, making managing RIS challenging. Surgery is the treatment of choice for this sarcoma. In metastatic disease, chemotherapy and targeted therapy may be used.

What Are the Atypical Presentations of Radiation-Induced Sarcoma?

Atypical imaging presentations of radiation-induced sarcoma make its diagnosis and management more challenging.

The following are some of the atypical presentations of radiation-induced sarcomas.

1)Unusual Location of Tumors - It can occur in any anatomical location, including locations not exposed to radiation therapy. In general, RIS arises within the radiation field of the original treatment, but in rare cases, it can develop in distant or contralateral sites. This uncommon location can confuse healthcare professionals when associating the tumor with prior radiation therapy, delaying diagnosis.

2) Rapidly Growing Masses - RIS can sometimes present with a benign appearance on imaging but shows features of cancer, such as growing rapidly and aggressively. This paradoxical behavior can confuse the diagnostic process. For example, an imaging study might suggest a benign lesion, but the clinical presentation, including rapid growth and pain, suggests a malignant process. This difference can result in delayed diagnosis and potentially compromise patient outcomes.

3) Variable Signal Intensity on MRI - Magnetic resonance imaging (MRI) is essential for distinguishing soft tissue lesions, including those related to RIS. However, RIS can exhibit changes in signal intensities (brightness or darkness of an area on an MRI image) on MRI, depending on the cancer type. Angiosarcomas may appear hyperintense (an area of high intensity on MRI) due to hemorrhage, while malignant fibrous histiocytomas (MFH) may show variations in signal intensity, making the diagnosis challenging. So, healthcare professionals should consider the changes in imaging appearances when evaluating soft tissue tumors in patients with a radiation therapy history.

4) Changes in the Radiation Field - The development of new tumors within the original radiation field is another atypical presentation of RIS. Radiation-induced sarcoma may sometimes be identified during routine follow-up with imaging tests. The presentation of new lesions within the radiation field, even if they are benign, should raise suspicion and warrant further investigation.

5) Difference in Imaging and Clinical Presentation - Radiation-induced sarcomas may show benign characteristics in imaging studies, such as well-defined, slow-growing masses that resemble benign tumors. These findings can mislead oncologists and radiologists, leading to delayed diagnosis and inappropriate treatment. With the history of radiation therapy in patients, healthcare professionals must remain vigilant and consider evaluating soft tissue masses, even if they appear benign and slow-growing on imaging.

What Are the Symptoms of Radiation-Induced Sarcoma?

The most common symptom of radiation-induced sarcoma is pain. This pain is sudden and continuous, which can become worse at night. The findings and symptoms are localized to the irradiated area in typical cases. Usually, the pain is not suppressed by any painkillers.

Clinically presentation that favors radiation-induced sarcoma diagnosis is

• Soft or bony mass.

• Bleeding may be present in some patients.

• Pathological fracture (fracture occurring due to underlying disease).

• Cancer in bone or soft tissue appears at an unusual age.

• Tumor in bone or soft tissue at an unusual site.

• History of intensive chemotherapy to irradiation.

How Is Radiation-Induced Sarcoma Diagnosed?

Diagnosing radiation-induced sarcoma is a complex process that often requires assistance from a multidisciplinary team. Oncologists, radiologists, surgeons, and pathologists must collaborate to reach an accurate diagnosis and develop a proper treatment plan.

• History and Physical Examination - A complete physician examination and detailed history of previous radiation therapy are crucial for diagnosing radiation-induced sarcoma. Physicians should enquire about the dose of radiation, its location, and duration for assessing the risk of RIS.

• Keeping Track of Imaging - Regular imaging follow-up can help detect RIS early, as they can grow rapidly in a short period. Keeping track of imaging can improve the chances of effective treatment.

• Biopsy - It is a procedure to collect cells, tissue, or fluid from the body for examination by a healthcare professional. A biopsy of the suspicious lesion will help to confirm the presence of malignancy, check for the histological subtype, and guide treatment decisions.

What Is the Treatment of Radiation-Induced Sarcomas?

The treatment of RIS is complex and challenging. Similar to diagnosis, treatment also requires input from a multidisciplinary team.

• Surgical Resection - Surgical resection is the primary treatment option for most RIS. To attain local control and improve the result of the treatment, complete resection of the tumor and negative surgical margins is essential. However, this can be challenging if the tumor is in a critical anatomical site.

• Radiation Therapy - Radiation therapy must be considered in some instances to improve local control or treat inoperable tumors. The factors to consider before using radiation therapy are tumor location, size, and histology, or it can cause increased toxicity to surrounding tissues.

• Chemotherapy - Chemotherapy is performed for patients with metastatic cancer that cannot be removed with surgical resection.

• Diet - Nutrition is essential to improving a patient's health and getting the best cancer treatment outcomes. Cancer treatments such as surgery, radiation therapy, and chemotherapy can alter the patient's ability to digest and absorb food, which may adversely affect the patient's nutritional status. Treatment with commercially available liquid nutritional supplements may be needed to maintain adequate caloric intake.

Conclusion:

Radiation-induced sarcomas are very rare but a severe complication of radiation therapy. Early diagnosis and prompt treatment can provide favorable outcomes. However, in the case of atypical imaging presentations, the diagnostic process can be confusing and misleading, causing delays in diagnosis and treatment. The healthcare team should be vigilant in diagnosing this condition if the patient has a previous history of radiation therapy, which can yield proper diagnosis and treatment to provide favorable outcomes.