Retinoblastoma+-+A+Child's+Cancer

Harold, a seven-month-old boy, has been having some abnormalities with his eye, which previously appeared to be functioning normally. The left one has become “lazy” and doesn’t move completely in sync with the right. Lately, when his parents take pictures of him, there’s also a weird glow in the left pupil. It’s like he has red-eye, but the glow is white and yellow in color instead. When his parents take him the doctor to have these abnormalities checked, the doctor suspects they’re symptoms of a cancer called retinoblastoma, so he refers Harold to an ocular ophthalmologist, who specializes in cancers of the eye.  Retinoblastoma is a rare cancer specific only to children, almost entirely younger than five. It makes up only two percent of childhood cancers, and only 250 to 300 children are diagnosed with it per year in the United States.  Retinoblastoma is a cancer of the retina, which is a thin membrane that lines the inside of the back of the eye. During early development, cells called retinoblasts divide and grow to fill the retina. Usually these cells stop growing after development, however, if a cell already carries a mutation of the retinoblastoma (//RB1// or //Rb//) gene and later acquires a second mutation, the cell will fail to halt division and has the potential to grow into a cancerous tumor. The usual function of the //RB1// gene is to prevent out-of-control cell growth. If undetected for long enough, the cancer can potentially spread to larger portions of the eye and tissue near to the eye.

 Through generating images of the eyes via ultrasound and MRI, the doctors discover Harold’s right eye is affected in addition to his left, although to a lesser degree. Harold has developed hereditary or bilateral retinoblastoma, which 40 percent of retinoblastoma patients have. When diagnosed, bilateral retinoblastoma patients can have cancer in one or both eyes, but if cancer has developed in both eyes it’s always considered bilateral. Although neither of Harold’s parents carry the //RB1// mutation, his cancer is still considered hereditary because the egg or sperm had to have carried the //RB1// mutation or the mutation had to have developed during pregnancy for Harold to develop bilateral retinoblastoma. This is actually the case for 80 to 90 percent of bilateral retinoblastoma patients. Both of Harold’s parents are in good health and neither has ever been exposed to high levels of radiation, carcinogens, or other mutagens, so the mutation is most likely attributable to bad luck. Bilateral retinoblastoma is generally diagnosed in the first year, like with Harold. He was predisposed to developing retinoblastoma, already having one //RB1// mutation. In the first few years of life, rapid growth occurs, including in the eyes. Harold’s cells, which already contained the //RB1// mutation, grew extremely quickly and because of the quick growth there was a higher probability a cell would acquire a second //RB1// mutation and a tumor would develop even before he was seven months old. Neither his gender nor his ethnicity predisposed him to this cancer since it occurs equally in males and females and among different races and ethnicities. Unfortunately, since Harold carries the mutated gene, he is also at risk for passing it on to his future offspring. There’s a 50 percent chance he will pass the mutated //RB1// gene to his descendants. Harold’s parents are told they have several treatment options including surgery, radiation, focal therapy, and chemotherapy. Focal therapy involves treatment of the affected eyes with lasers or freezing therapy. Further analysis of the tumors, however, is needed to determine the most promising methods of treatment.

 Harold’s future is optimistic given over 95 percent of children survive retinoblastoma in the developed world, and 70 to 80 percent of eyes are saved in patients with both eyes affected. This is largely due to early detection and treatment post-remission. The outlook is also promising because the cancer is intraocular and contained in the eyes and hasn’t yet become extraocular and spread outside of the eyes. In the United States, most children are diagnosed before the cancer has spread outside of the eye. Additionally, the five year survival rate for retinoblastoma is 97 percent from birth to age fourteen. Post-treatment there will still be a risk of future cancers, especially because Harold’s cancer was hereditary. He only has one normal copy of the //RB1// gene, and another future mutation could lead to new tumor growth. Follow-up check-ups and eye exams in the first few years post-cancer will help monitor for potential new tumor growth. Regular MRI scans to check for trilateral retinoblastoma, which occurs when a tumor develops in the brain as a result of bilateral retinoblastoma, will also be important. Scans are recommended for five years post-cancer. Even beyond that, Harold will always have to be vigilant in checking for new cancer development.

=Treatment=  After receiving a referral to Johns Hopkins Medical Center, Harold’s parents sit down with a pediatric oncologist to discuss the best options to treat Harold’s bilateral retinoblastoma. She is one of many doctors who will be part of Harold’s team during treatment. Other doctors will include a pediatric ophthalmologist who specializes in children’s eye diseases and an ocular oncologist who specializes in cancers of the eye. The pediatric oncologist first assures the parents that they’ve caught Harold’s cancer early enough that his future looks promising. She explains how for most cancers, doctors perform a biopsy on the tumor, removing part of it for examination, however, because retinoblastoma occurs in the eye, this is hardly even done for fear of damaging the eye. There’s an additional risk of disturbing the tumor, causing some cancer cells to come loose from it and spread to other areas of the body. Images generated by ultrasound and MRI provide high quality imagery of the tumors and show that Harold’s cancer is still contained in his eyes. The primary objective is to help Harold recover while saving as much of his vision and his eyes as possible.

 Enucleation, which is surgery to remove the eye and part of the optic nerve, is off the table. Harold’s doctor doesn’t believe the treatment needs to be that aggressive, and enucleation would mean Harold would lose his vision. External radiation therapy, or radiation applied to Harold using a linear accelerator that emits a high-energy beam of photons, is also ill-advised in his case. Harold has bilateral retinoblastoma which means all of his cells contain only one good copy of the //RB1// gene, and exposure to radiation could potentially cause the normally functioning //RB1// gene, which regulates cell growth, to mutate in another cell. This could lead to uncontrollable cell growth in the mutated cell and the development of a new cancer.

 Although external radiation therapy is not recommended, brachytherapy or plaque radiotherapy is a potential treatment option. It’s a type of internal radiation therapy where a small amount of radioactive material is placed in a small carrier called a plaque. The plaque is shaped like a small bottle cap and made out of lead or gold to shield non-targeted tissue from radiation. It’s then attached via surgery to the outside of the eye but adjacent to the tumor. This focuses radiation on the tumor, and the radiation should only affect the tumor because it travels very short distances. There are two surgeries to attach and remove the plaque, both within a few days of each other. Harold would have to stay at the hospital for the duration of this time, and the tumors in both eyes would be treated. Overall, brachytherapy is an excellent treatment option because it is not linked to the development of a second cancer, which is a major worry for Harold. There is some concern that the treatment could damage his retinas or optic nerves. Loss of vision or impaired vision is the main side effect of damage, but vision loss may not manifest itself until many months later. Luckily, damage has occurred less and less as the method has advanced.

 Another option is thermotherapy or transpupillary thermal therapy. It would serve the same purpose as brachytherapy but is an alternate method of destroying the tumors. An infrared light laser is used to target a tumor and precisely heat it. Harold would be asleep for this, and each treatment would last fewer than ten minutes. The treatment would occur three times with a month between each session. Possible side effects include shrinking of the iris, clouding of the eye and damage to the retina, all of which would impair vision. These side effects would be a result of non-tumorigenic tissue coming in close contact with the laser for too long. Before brachytherapy or thermotherapy is carried out, however, Harold’s doctor suggests trying chemotherapy to shrink the tumor in the left eye because it is the larger of the two. This will help ensure treatment is maximally successful.

 Chemotherapy drugs attack quickly dividing cells, like those in tumors. Unfortunately this could also affect Harold’s mouth, stomach, hair, and bone marrow cells because they all divide rapidly. As a result, side effects, which include loss of hair and appetite, nausea, easy bruising and bleeding, and increased risk of infection due to white-blood cell loss, could occur. It helps though that Harold is a child and children generally have less severe side effects compared to adults. For chemotherapy treatment, Harold has two options. He can receive systemic chemotherapy which is administered intravenously or orally. The chemotherapy drugs will circulate in his bloodstream reaching his entire body. The second option is a newer option but highly recommended. It’s called intra-arterial chemotherapy. Chemotherapy drugs are infused into the ophthalmic artery, the main artery leading to the eye. This is done by inserting a catheter, which is a long and very thin tube, into a large artery in the inner thigh. The catheter is then carefully threaded through the blood vessels all the way to the ophthalmic artery where the drugs are infused. The treatment would of course be done under anesthesia and repeated every few weeks, depending on how much the tumor has shrunk. Because intra-arterial chemotherapy is highly targeted, its side effects are less severe. Less than ten percent of the drugs used for systemic chemotherapy would be applied each time. Treatment would use a drug called melphalan hydrochloride. Usually used to treat multiple myeloma, a cancer of the bone marrow, melphalan is good for intra-arterial chemotherapy because it’s a chemotherapy drug that can be dissolved in fluid and administered intravenously. Harold is lucky Johns Hopkins Medical Center is offering this treatment already since it is not very widespread yet, and some clinical trials are still underway involving different variations of treatment. Currently there are only two National Cancer Institute-sponsored clinical trials related to retinoblastoma going on in the United States, neither of which Harold is eligible for, so intra-arterial chemotherapy is the most progressive treatment available.

 Harold’s parents, after weighing the options, decide to choose intra-arterial chemotherapy combined with thermotherapy because they believe it is the most promising treatment combination. Although brachytherapy isn’t implicated in causing secondary cancers, the idea of using radiation when Harold is already prone to a second cancer in his lifetime worries them. They also think thermotherapy sounds less invasive because it does not require surgery. Harold’s pediatric oncologist approves this course of treatment and believes that she can successfully work with other healthcare professionals to cure Harold of retinoblastoma, allowing him to grow up and be a happy and healthy child.

=Looking Deeper - The Molecular Basis=  After deciding on a course of treatment, Harold’s parents seek to learn more about how the //RB1// gene mutation developed which led to his cancer and how the treatments will work to destroy the tumor. They ask his doctor, and she decides to cover how the treatments work first because they are much more straightforward. Thermotherapy is relatively simple on a molecular level. Infrared radiation is applied to the eye through a diode laser. The laser diameter will span the tumor but will not extend anywhere outside to normal tissue. When activated, the laser will heat the tumor to over 45 degrees Celsius, well above the optimal temperature for a cell. Heat at 45 degrees Celsius is cytotoxic to cells. As a result, essential proteins and DNA in the tumor cells will de-nature at such a high temperature and cell death will occur. Thus over several sessions, the tumor will gradually shrink more and more as outer layers of the tumor are treated with thermotherapy and cells die.

 With intra-arterial chemotherapy, a microcatheter is placed at the opening of the ophthalmic artery which is the major artery leading to the eye. Once there, a small dose of the chemotherapy drug is released. Harold’s treatment will use melphalan, an alkylating agent, as the chemotherapy drug. Alkylating agents replace the hydrogen atoms on DNA with alkyl groups. This causes crosslinking within the DNA and interferes with the transcription of DNA to RNA and subsequent protein synthesis. Melphalan specifically targets the N7 position of the DNA nucleotide base guanine and covalently binds to it. The drug can also bind to a guanine on the opposite DNA strand causing inter-strand cross-linkages. This prevents DNA from opening, and genes affected by cross-linkages can no longer be transcribed. Synthesis of new DNA is also not possible because the two strands can’t be separated. This is cytotoxic to the cells, and although all cells in the area will be affected and potentially undergo apoptosis, rapidly dividing tumor cells will be especially impacted. They are so focused on rapid division that they do not repair DNA as well as cells growing at a normal rate. As a result, many of the tumor cells are unable to replicate their DNA and effectively divide, halting tumor growth and causing cell death in cells affected by melphalan.

 The doctor then moves on to explain how Harold developed the //RB1// mutation and consequential retinoblastoma. She tells them that the //RB1// gene is on chromosome 13 and explains that the original tumor cells would have undergone two mutations to end up carrying only the recessive alleles of //RB1//. Because Harold has hereditary retinoblastoma, the first //RB1// mutation would have occurred prior to birth and the second after birth. It’s likely that at least one mutation in the gene was a missense mutation because those are prevalently found in hereditary retinoblastoma. A missense mutation is when a nucleotide mutates so the codon read during translation no longer codes for the same amino acid, and that can drastically affect the protein created. Exons are sections of DNA that code for proteins, and sixty percent of //RB1// missense mutations occur in exons 19-21 which contain the coding for cyclin box B. The section is named cyclin box B because it codes for a subdomain of the protein that will fold similarly to how some sections of cyclin proteins fold (cyclins are a group of proteins that regulate the cell cycle). Cyclin folds are typically involved in protein-protein interactions,  so a mutation in this section of the gene could lead to a non-functioning protein or one that is damaged enough that it can’t interact with other proteins properly. In cancer, this would likely mean a mutation in a cyclin box B exon has caused a mutation in the //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">RB1 //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> protein. Since //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">RB1 //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> is a growth suppressing gene, the mutation likely disrupted a signaling pathway that would’ve ultimately told the cell not to divide. This disruption would eventually lead to unsuppressed growth. Although missense mutations are prevalent in hereditary retinoblastoma, most gene mutations seen are actually nonsense point mutations, meaning the mutation of one nucleotide has created a pre-mature stop codon that halts translation early and leads to an incomplete protein. Based on the database of //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">RB1 //<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> gene mutations (RBGMdb), 302 out of 932 nonsense point mutations catalogued in retinoblastoma are recurrent. Even more interesting, 79 percent of recurrences are mutations of cytosine to thymine in CGA codons found in eight specific exons. <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> This implies that cytosine may be especially vulnerable to mutation, especially cytosine that is part of a CGA codon. Four of the exons with frequent cytosine mutations also have a high frequency of methylation on bonded cytosines and guanines. <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> Methylation means that many methyl groups have bound to these areas of DNA, specifically the 5’ position of cytosine, and methylation is associated with the inhibition of genes. In some cases methylation can directly affect the binding of the transcription factor, thus inhibiting gene transcription; in other cases the cause of inhibition is indirect and the exact causes are not yet clear. <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> The presence of many mutations in areas of high methylation implies these regions may be more prone to mutations that lead to retinoblastoma. Cytosine in general may also be particularly vulnerable to cancer-causing mutations, and this is likely linked to methylation.

<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> The protein coded in the gene is called p110 <span style="font-family: Arial,Helvetica,sans-serif; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">, and it helps regulate cell growth. The p110 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> protein produced from transcription and translation of the gene is what allows the gene to act as a tumor suppressor. In the cell cycle in the G <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: sub;">0 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> phase and early in G <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: sub;">1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> phase, p110 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> is hypophosphorylated, meaning it does not have very much phosphorous bound to it. Later in the G1 phase and in S phase (synthesis), the amino acids serine and threonine become phosphorylated, leading to phosphorylated p110 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">. The presence of the phosphorylated form triggers a signaling cascade that tells the cell to replicate its DNA and divide. It’s the hypophosphorylated form of p110 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">, however, that’s considered active, preventing cell division and activation of the pathway that would promote growth and division of the cell. Most mutations of the gene lead to truncated or unstable proteins which fail to work properly, leading to a tumor if both alleles are mutated. The importance of the p110 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5; vertical-align: super;">RB1 <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> protein is also supported in the failure to detect the protein in any RB tumors, implying the loss of the protein helped promote the tumor.

<span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;"> Luckily for Harold, after the first few years of life, retinal cells cease to divide which means the risk of a tumor developing is eliminated. Non-retinal cells will continue to grow, but they’re often inhospitable environments for RB tumors to develop. The lack of tumor formation is possibly due to the cells being unaffected by the loss of the gene or the mutation may be lethal to non-retinal cells. Either way, once Harold is cured of retinoblastoma and has reached age four, he should be safe from the cancer returning. He must still be vigilant about checking for other cancers, however, because he is still predisposed to a variety of cancers.

=Looking to the Future= <span style="color: #222222; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; line-height: 1.5;">At the end of their meeting, Harold’s doctor reassures his parents that she and the rest of his care team will be there to support them throughout the treatment. She understands that while Harold may be too young to understand what is going on, his parents certainly do and may still be in shock from the diagnosis. She also lets them know that they are not alone, although it may feel like that at first. Their hospital has a database of past families who dealt with retinoblastoma and are willing to reach out and talk to Harold’s parents about what they’re going through. They can uniquely understand the situation and will provide a different kind of support than family members and friends can. The families can also share their experiences to help Harold’s parents better understand what to expect in the coming months. Harold’s doctor also recommends reaching out to the American Cancer Society which organizes support groups for families with children with retinoblastoma. On a final note, she tells the parents that although they may feel worried and scared now, they should also try to remember they are lucky they caught the cancer early. The five year survival rate is 97 percent, and on the whole, Harold’s future looks bright.

=<span style="font-family: Arial,Helvetica,sans-serif;">Aperçu = <span style="color: #222222; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; line-height: 1.5;">"Treasure the time you spend with your child but also remember the five year survival rate is an incredible 97 percent; children may be young, but they’re tougher than you think."