Thankfully, kidney tumors are rare in children, with some of them being highly treatable and usually curable. But would you know how to recognize this condition? The following information should help you spot this tumor long before it becomes a life-threatening issue.

What can I expect under normal conditions?

Most people have two kidneys. The kidneys produce urine, which drains through narrow tubes (called ureters) into the bladder. The kidneys are located toward the back of the flank, with one kidney on either side. The main function of the kidney is to produce urine. However, the kidney accomplishes many other important functions during urine production. By adjusting the composition of the urine, the kidney regulates the body’s electrolytes, fluid balance and pH balance, and eliminates certain waste products made by the body.

What are the signs of a problem?

A lump in the child’s abdomen may be felt during bathing, dressing or other daily activities, or during a routine physical examination by the pediatrician. Occasionally, the child will develop symptoms such as blood in the urine (hematuria), abdominal pain, fever, reduced appetite, weight loss, constipation or high blood pressure (hypertension).

What are the different types of renal tumors in children?

Wilms’ tumor: Also referred to as nephroblastoma, this is the most common form of kidney cancer in children. The incidence of Wilms’ tumor is 8.1 cases per million in white children less than 15 years of age. Wilms’ tumor represents 5 to 6 percent of childhood cancers in the United States where 450 to 500 cases per year occur annually. Wilms’ tumor occurs slightly more often in girls other than boys. The mean age at diagnosis of Wilms’ tumor is 41.5 months for boys and 46.9 months for girls.

Renal cell carcinoma (RCC):  Also called renal adenocarcinoma or hypernephroma, it is the development of cancerous changes in the cells of the renal tubules. RCC is more common than Wilms’ tumor after the age of 10 years. However, it is far less common overall than Wilms’ tumor. This cancer spreads easily (metastasizes), most often to the lungs and other organs, with about one-third of cases diagnosed after the tumor has already spread.

Congenital mesoblastic nephroma: This tumor is usually discovered during the first three months of life and is believed to be existing at birth. It is the most common renal tumor of early infancy.

What causes renal tumors?

There has been considerable interest in the genetics behind the development of renal tumors in children. Specific chromosomal abnormalities have been identified that appear to show an increased risk for Wilms’ tumor. Much work continues to be done to evaluate other chromosomal abnormalities that can lead to the tumor’s growth and those that are responsible for its behavior. Researchers are hopeful that this information might provide some insight for treatment of the disease.

Why are tumors classified by stage?

The type of tumor found through pathological examination is very predictive of the outcome of children with renal tumors. For instance, Wilms’ tumors are separated into favorable and unfavorable types — a key distinction because unfavorable types do not respond as well to the standard chemotherapy. The determination of tumor type is very important so that the children can receive the appropriate therapy.

As with most tumors, a staging system has been developed to stratify patients for treatment. Patients with tumors confined to the kidney that can be removed completely have the best survival rate. This is most notable for the patients who have unfavorable microscopic tissue structure. The tumors in these patients are not very responsive to chemotherapy or radiation therapy and complete removal is essential.

Stage I: Tumor limited to kidney, with complete removal

Stage II: Tumor through kidney capsule but completely removed, local spillage of tumor, tumor in kidney vein

Stage III: Local lymph nodes positive, diffuse spillage of tumor, positive surgical margin

Stage IV: Metastases to lung, liver, bone, or brain

Stage V: Bilateral tumor

The unfavorable microscopic tissue structure variants of Wilms’ tumor fall into three categories: anaplasia, clear cell sarcoma and rhabdoid tumor of the kidney. Of the three, only clear cell sarcoma has been responsive to chemotherapy. Renal cell carcinoma that occurs later in childhood is not chemosensitive, much like the adult tumors.

How are renal tumors diagnosed?

Once a child presents with an abdominal mass, they undergo radiologic studies. Most children have an ultrasound that can determine if the mass originates from the kidney and whether it is a solid tumor. Following this, children are evaluated with either a CT scan or an MRI. These studies are done with the intent of identifying the extent of the tumor and whether it has spread to other organs. Wilms’ tumor can extend into the vascular system and it is important to identify this preoperatively. Wilms’ tumor can also occur in both kidneys. About 5 percent of all patients have bilateral Wilms’ tumor at diagnosis. If bilateral tumors are recognized on the diagnostic studies, it will change the initial management approach. It is very important to determine that the kidney is not involved with the tumor and is functioning normally. Other studies are done to examine the lungs to insure no harmful tumors are present. The lungs are the most common site of tumor spread outside of the kidney. A chest X-ray will identify most abnormalities, but some smaller lesions are only seen on a CT scan.

The unfavorable tumor types, such as clear cell sarcoma and rhabdoid tumor of the kidney, can spread to the bones. The same is true for renal cell carcinoma. Rhabdoid tumor of the kidney can also spread to the brain. Therefore, bone scans and MRIs of the brain are obtained in these select patients.

What are some treatment options?

The primary treatment of all renal tumors in children is surgical removal. For most patients, this consists of a radical nephrectomy wherein the tumor and entire kidney are removed. During the operation, an exploration is performed to determine if the tumor has spread outside of the kidney. This includes the regional lymph nodes and the liver. It is very important to determine if the tumor is confined to the kidneys. Wilms’ tumors are very soft and can rupture both before and during surgery. This rupture is documented as it can change the stage of the disease and increase the risk of recurrence after surgery.

In patients with tumors in both kidneys, it is advisable that neither kidney be removed at the initial surgery. To start, a biopsy of the tumor is obtained to help determine the tumor type. The patient then receives chemotherapy. The goal is to reduce the size of the tumors. At a later date, the patient is taken back into surgery to remove just the tumor and a portion of the kidney, saving most of both kidneys to maintain normal kidney function. This type of approach is more feasible for the favorable Wilms’ tumor and should not be used for tumors withanaplastic microscopic tissue structure.

Congenital mesoblastic nephroma, which occurs in infants, is generally treated with surgery alone. For most patients this is curative. There are some children who have unusual histologic types that have been known to spread outside the kidney. This is more common in those diagnosed after the age of three months. In these select cases, some consideration for treatment with chemotherapy after surgery is needed. Renal cell carcinoma is also primarily treated by surgery not because this is always curative, but because there is really no effective adjuvant therapy like chemotherapy available. The tumors that are confined to the kidney have the best outcome.

What can I expect after treatment?

Following surgery, most patients with Wilms’ tumor receive chemotherapy and a select number of patients receive radiation therapy. The standard chemotherapy regimen administered to Wilms’ tumor patients is dactinomycin and vincristine. After the introduction of these chemotherapy agents 30 years ago, the survival of patients with Wilms’ tumor improved dramatically. With surgery alone, survival was only 25 percent. With chemotherapy, the survival approaches 90 percent for all patients with Wilms’ tumors.

Patients are treated with chemotherapy for varying lengths of time. Children who have their entire tumor removed receive chemotherapy for six months. If there is residual disease or spread of tumor elsewhere, a child will receive additional therapy, including the drug doxorubicin. These patients also receive radiation therapy depending on the location of tumor spread. This added therapy is necessary to achieve the current improved survival. However, there is some increased risk of side effects with the increased therapy used in these treatment regimens. Patients with unfavorable tumor types have not had an improvement in survival over the past few decades. Research continues to be conducted to identify chemotherapy drugs that might be of proven benefit in these children.

Wilms’ tumors tend to recur in several sites, including the lung, liver and the local surgical area. New tumors can later develop in the opposite kidney, but patients with that risk can usually be identified from their initial pathologic findings. There are lesions in the kidney that are known to be precursors to the development of Wilms’ tumor. If they are present at the time of the initial nephrectomy, those patients need to be monitored very closely. Frequent imaging of the remaining kidney is performed to detect tumor recurrence. Theoretically, recurrent tumors will be smaller and can be more easily managed with a conservative approach designed to spare the kidney.

The most frequent site of recurrent disease is the lung. The time of recurrence is important.  Patients with early recurrence during the course of chemotherapy have a worse outcome.  Patients who develop an abdominal recurrence or those receiving prior radiation who develop recurrence also have a worse prognosis.

Late effects of treatment are inevitable, as there are some risks involved in the therapies used to treat all malignancies. Children may be at greater risk because their bodies are still developing at the time that therapy is given.

Musculoskeletal problems were more commonly seen in early days of treatment of renal tumors.  Most of these effects were due to upper body radiation. The patients developed curvature of the spine and the tissue exposed to radiation failed to grow. Over time, the amount of radiation therapy administered to children with Wilms’ tumor has decreased and the musculoskeletal defects have been less notable.

A particular concern is the development of other cancers in children who have been successfully treated for Wilms’ tumor. These have occurred in the bone, breast and thyroid.  Patients who initially receive radiation therapy and those who have been treated with doxorubicin have the greatest risk. The incidence of these secondary malignancies is increasing with longer follow up. All children enrolled in clinical trials for treatment of renal tumors are followed intensely throughout their lifetime. Information gained from long-term follow up will help determine the treatments responsible for late effects. Information will then be used to modify current treatment guidelines.

Other late effects of therapy include decreased fertility. This is more notable in patients who receive radiation, particularly to the abdominal area. Both ovarian failure and testicular failure have occurred. Kidney function is also a concern in children who have had one of their kidneys removed. Although studies suggest that long-term dysfunction is minimal, further follow up is clearly necessary.

Frequently Asked Questions

What are some risk factors for Wilms’ tumor?

The exact cause of tumor formation is unknown but it has been associated with certain birth defects including urinary tract abnormalities, Bethwith-Wiedemann syndrome, aniridia and hemihypertrophy. Wilms’ also has an increased incidence among siblings and twins, which suggests a possible genetic cause.

What is the chance that my child will be cured?

It depends on the type, stage and location of the renal tumor. Wilms’ tumor has a high cure rate with treatment. Currently, more than 90% of children with favorable histology tumors are survivors.  The outcome of patients with renal cell carcinoma varies depending on the amount the tumor has spread. The five-year survival rate is around 60 to 75 percent if the tumor is in the early stages. If it has spread to the lymph nodes, the five-year survival rate drops to between 5 and 15 percent. If it has spread to other organs, the probable outcome is poor with a five-year survival rate at less than 5 percent.

What are the complications of Wilms’ tumor?

Spreading of the tumor to the lungs, bone or brain are the main complications. Removal of a bilateral tumor may leave the patient with minimal kidney function.

Will there be anyone to help?

Absolutely! One of the most magnificent aspects of the institutions participating in large children cancer treatments is the commitment to family-centered care. You will be supported by hospital personnel who are trained to deal with families of children with cancer. Furthermore, there will be multiple other families who are going through the same thing you are. Each of you will be able to give the other significant support.

Source: Urology Care Foundation