Radiation Therapy in Rare Tumor Types - An Overview

Introduction:

Rare cancer types are those whose incidence is very low, and due to their low prevalence, research is limited, making precise target delineation challenging. This involves determining the amount of dose to be delivered and its uncertain late effects. Radiation therapy is one of the types of cancer treatment that is highly effective, with good survival rates and tolerance. This article discusses the use of radiation therapy in the management of rare cancer types. Please read below to know more.

What Is Radiation Therapy?

Radiation therapy (RT), also called radiotherapy, is a type of cancer treatment that uses a high dose of radiation to damage the cancer cells present in the body. It is the most commonly used treatment, either as a primary treatment or in combination with chemotherapy or surgery. This radiation therapy employs a precise amount of radiation to kill cancer cells while minimizing damage to healthy cells. There are two types of radiation therapy:

1. External Beam Radiation Therapy: This involves the use of a machine to target high-energy radiation beams at the cancers or tumors from outside the body.

2. Internal Radiation Therapy: This involves the placement of radiation sources directly near the tumor or cancer sites, with a limited range of radiation that spares the healthy cells and targets the cancer cells.

How Is Radiation Therapy Used in Rare Tumor Types?

Rare tumor types are uncommon tumors with low prevalence and are infrequently diagnosed among the general population. These tumors have limited knowledge about their biology and limited treatment strategies. Some of the rare tumor types in which radiation therapy is used include:

1. Mucosal Melanoma: It is a rare tumor that occurs in the upper aero-digestive tract, which includes the respiratory and digestive tracts, and it has a poor prognosis. These tumors are mostly found in the nasal cavity and paranasal sinuses. In oral cavity cases, they may also involve neck lymph nodes. Radiation therapy is used as an adjuvant treatment, given in conventional fractionation with 2 Gy (Gray) per fraction to a total postoperative dose of 60 to 66 Gy. In cases with neck involvement, a hypofractionated schedule is given, delivering larger doses of radiation in fewer treatment sessions. For locally advanced tumors, different types of radiation therapy are used, such as brachytherapy (a type of internal radiation therapy in which a radioactive source is placed near the tumor), external photon or electron beam RT (a type of external radiation therapy in which high-energy beams of electrons or photons are used to kill the cancer cells), and intraoperative RT (IORT, where high radiation is delivered to the tumor site in the operating room itself). Carbon ion therapy (high-energy carbon ions are used to kill cancer cells) shows minimal toxicity and good local control rates.

2. Trachea Tumor: These are rare tumors, accounting for only 2 percent of upper airway tumors. Most of these tumors are squamous cell or adenoid cystic carcinomas (ACCs). The most common treatment for ACCs is surgery, and radiation therapy can be used as an adjuvant. The role of radiation therapy is not well defined, but it has a positive impact on the overall survival rate of 88 percent. Definitive radiotherapy for unresectable tumors has shown long-term survival. Failure in tracheal ACC is mostly due to lung metastasis.

3. Neuroendocrine Tumors: These are tumors that form in specialized hormonal cells, which release hormones into the blood and receive signals from the brain. Although surgical resection with negative margins is the primary treatment for localized pancreatic neuroendocrine tumors (PNET), radiation therapy can be used as a post-surgical treatment, and stereotactic radiotherapy (SBRT, where a high dose of radiation is targeted in fewer sessions) can be used, which employs a narrow beam of radiation. In the case of anorectal neuroendocrine tumors (cancer that occurs from neuroendocrine cells present in the anus or rectum), RT-CT (radiotherapy combined with chemotherapy) can eliminate the need for a definitive colostomy (a surgical procedure in which an opening is made in the abdominal and a portion of the large intestine is brought to the surface).

4. Hepatobiliary Tumor: It is a type of cancer that involves the liver and can be linked to non-alcoholic fatty liver disease, chronic hepatitis C infection, and obesity. Surgical resection is the primary treatment, but in cases where surgery is not possible, radioembolization (an RT in which small particles of radioactive particles are injected into the blood vessels of the tumor to kill the cancer cells), transarterial chemoembolization (a procedure in which chemotherapy drugs are injected in the blood vessels of the tumor cells), and SBRT are considered. SBRT has shown positive outcomes as a treatment option. Additionally, adjuvant radiotherapy is beneficial for postoperative cases of gallbladder carcinoma and extrahepatic CCA (extrahepatic cholangiocarcinoma, which occurs in the bile ducts present outside the liver).

5. Soft Tissue Sarcoma and Desmoid Tumor: Soft Tissue Sarcomas are rare cancers, accounting for less than 1 percent of all cancer cases. Surgical excision is the primary treatment for localized soft tissue sarcomas, while postoperative radiotherapy is often used for advanced cases. Intensity-modulated radiotherapy (IMRT), which is a type of external beam radiation therapy, a new technology, has shown promising results in the treatment of soft tissue sarcomas. IORT is used as an alternative treatment for high-risk cases with a high chance of recurrence. Desmoid tumors occur due to mutations in the b-catenin gene, and radiotherapy is indicated in cases where surgery is not feasible, and symptoms are present. Adjuvant radiotherapy can also reduce the risk of relapse that may occur after inadequate surgery.

6. Ovarian Cancer: The primary treatment for epithelial ovarian cancer includes cytoreductive surgery along with chemotherapy using taxane and platinum compounds. Recurrence is observed in 70 percent of cases, and the use of whole-abdominopelvic irradiation has shown poor outcomes. However, SABR has demonstrated better results. Therefore, radiotherapy can be considered in cases of recurrent-progressive disease.

7. Endocrine Tumor: Adrenocortical carcinoma is a rare endocrine cancer with a poor prognosis. Radical surgery is the primary treatment, but local control rates are only 19 to 60 percent. Therefore, adjuvant radiotherapy can reduce the local recurrence rate. Stereotactic ablative radiotherapy is effective in cases of non-resectable adrenal primitive or metastatic tumors. For pineocytomas (slow-growing brain tumors that occur in the pinealocytes cells), stereotactic radiosurgery can be used as an alternative to resection. For pineoblastomas (aggressive brain tumors that occur from the pineal gland), combined therapies such as radiotherapy, chemotherapy, and surgery have shown improved results.

Conclusion:

While radiation therapy is effective, it can also have many side effects, such as skin changes, hair loss, nausea, vomiting, fatigue, weight changes, diarrhea, loss of appetite, reduced blood cell counts, and even secondary cancers (which may occur with long-term treatment). However, it also offers potential benefits, such as organ preservation and local control in the context of radiation therapy. Individuals diagnosed with rare tumor types can find hope and improved outcomes through the significant promise held by radiation therapy.