Hep B Blog

Category Archives: Hepatitis B Prevention

Journey to the Cure: What Does Liver Cancer Research Look Like? ft. Aejaz Sayeed, PhD

Welcome to “Journey to the Cure.” This is a web series that chronicles the progress at the Hepatitis B Foundation and Baruch S. Blumberg Institute towards finding the cure for hepatitis B.

In the fourth episode (part 2), Kristine Alarcon, MPH sits down with Aejaz Sayeed, PhD, Assistant Professor at the Baruch S. Blumberg Institute, to talk about his research in liver cancer. For any questions about hepatitis B, please email info@hepb.org.

Disclaimer: The information provided in this audio post is not intended to serve as medical advice of endorsement of any product. The Hepatitis B Foundation strongly recommends each person discuss this information and their questions with a qualified health care provider.

Edited by:
Kristine Alarcon, MPH

Special thanks:
Samantha Young

Music:
Modern – iMovie Library Collection

Script:

Welcome to “Journey to the Cure!” Every month, we’ll sit down with scientists from the Hepatitis B Foundationand the Baruch S. Blumberg Instituteto talk to you about hepatitis B and efforts to find a cure for hepatitis B. There’s still a long way to go, but we’re here to walk you through our journey.

Kristine Alarcon, MPH:
Can you tell me about your research?

Aejaz Sayeed, PhD:
That’s an interesting question. I’vespent a lot of time pursuing breast cancer and prostate cancer. I just started working on the liver cancer. There are millions of people who are pursuing cancer research, but the challenge is that we have done a lot of progress in some cancers, but some cancers, still, we do not have a handle on. For example, we have done a lot of progress in breast and prostate cancer. We have not done much in pancreatic and liver cancer. And, the five-year survival rates of breast and prostate and other cancers have drastically increased, but we have not done much of a progress in pancreatic or a specific form of brain cancer or pancreatic cancer or liver cancer. The problem, again, is that we’re not able to detect the disease at an early stage, and if we had a good set of biomarkers available, there’s a good opportunity, there’s a good chance that we should be able to control these diseases as well.

Kristine Alarcon, MPH:
What attracted you to studying liver cancer?

Aejaz Sayeed, PhD:
I’ve been working on breast cancer and prostate cancer, so in liver cancer, I want to use the tools and techniques, which I used in breast and prostate cancer. That’s why there’s that desire to use the similar strategies, which I used in breast and prostate cancer to discover and characterize markers. That’s why I’m still setting up collaborations with transplant surgeons because liver cancer is treated generally by either resecting the tumor or transplanting the liver. The liver is such an important organ that you cannot really take the liver away. You need the liver. Transplanting the liver is another strategy of treating these patients, so, yes, it is basically that desire that we have more biomarkers, and I can use the knowledge that I gained in breast and prostate to recapitulate the same kind of events, so that we can make a dent.

Kristine Alarcon, MPH:
Yeah; that’s so cool.

Aejaz Sayeed, PhD:
Thank you.

Kristine Alarcon, MPH:
Well, thank you for joining us on this episode of “Journey to the Cure.” Please join us next time for our next episode. Thank you for joining us!

Aejaz Sayeed, PhD:
Thank you!

Journey to the Cure: How is Hepatitis B Related to Liver Cancer ft. Aejaz Sayeed, PhD

Welcome to “Journey to the Cure.” This is a web series that chronicles the progress at the Hepatitis B Foundation and Baruch S. Blumberg Institute towards finding the cure for hepatitis B.

In the four episode (part 1), Kristine Alarcon, MPH talks with Aejaz Sayeed, PhD, Assistant Professor of the Baruch S. Blumberg Institute. They talk about how hepatitis B is connected to liver cancer and doctors and scientists tell if a patient has cancer.

For any questions about hepatitis B, please email info@hepb.org.

The Hepatitis B Foundation is a national nonprofit organization dedicated to finding a cure and improving the lives of those affected by hepatitis B worldwide through research, education and patient advocacy. Visit us at www.hepb.org, on Facebook at www.facebook.com/hepbfoundation, on Twitter at @hepbfoundation, and our Blog at www.hepb.org/blog

Disclaimer: The information provided in this video is not intended to serve as medical advice or endorsement of any product. The Hepatitis B Foundation strongly recommends each person discuss this information and their questions with a qualified health care provider.

Edited:
Kristine Alarcon, MPH

Special thanks:
Samantha Young

Music:
Modern – iMovie Library Collection

 

 

Journey to the Cure: Where Can I Find Hep B Info Online? ft. Maureen Kamischke

Welcome to “Journey to the Cure.” This is a web series that chronicles the progress at the Hepatitis B Foundation and Baruch S. Blumberg Institute towards finding the cure for hepatitis B.

In the third episode (part 2), Kristine Alarcon, MPH sits down with Maureen Kamischke, Social Media Manager for the Hepatitis B Foundation, to talk about her social media work at the Foundation. For any questions about hepatitis B, please email info@hepb.org.

Disclaimer: The information provided in this audio post is not intended to serve as medical advice of endorsement of any product. The Hepatitis B Foundation strongly recommends each person discuss this information and their questions with a qualified health care provider.

Edited by:
Kristine Alarcon, MPH

Special thanks:
Samantha Young

Music:
Modern – iMovie Library Collection

 

Script:

Welcome to “Journey to the Cure!” Every month, we’ll sit down with scientists from the Hepatitis B Foundationand the Baruch S. Blumberg Institute to talk to you about hepatitis B and efforts to find a cure for hepatitis B. There’s still a long way to go, but we’re here to walk you through our journey.

Kristine Alarcon, MPH:
You are our social media manager, and I know you have also shared your hepatitis B story. You can find Maureen’s story in our #justB campaign. But, can you tell me more about your work as a social media manager?

Maureen Kamischke:
At the Foundation, we are very active on three outlets: Twitter, Facebook, and Instagram. On Twitter, we have over 6,000 followers. We have a very active Facebook community. I would really encourage people to check out these outlets. It’s a great place to just check out what’s going on: drugs and the status of them on a daily basis. Basically, those are being updated every day.

Kristine Alarcon, MPH:
So, why is social media so important to conveying hepatitis B information?

Maureen Kamischke:
So, I think social media is a great way to reach out to different audiences. I think it’s a great way to get the messages out. You know, you can put messages out; you can link back to different parts of our website that really need to be featured and highlighted so that there are areas of what people want to learn more about; and then of course, if you are really interested in the most recent articles in hepatitis B, it’s an easy enough to link out to those so that you are not doing the work for it.

Kristine Alarcon, MPH:
So, it’s just like another type of way to easily disseminate information and get it more widely available to everyone.

Maureen Kamischke:
Yes.

Kristine Alarcon, MPH:
So, you’ve made so many connections across the globe in regard to hepatitis B partnerships, so what do you think the future looks like in the elimination of hepatitis B?

Maureen Kamischke:
Well, I would have to say that on behalf of myself and all of our friends around the world, we’re all waiting for the cure, but until that time, there’s a lot that we can do. We have a lot of good treatments available. There’s a lot of information that needs to be disseminated. There are a lot of issues with stigma and discrimination. And hopefully, social media can help decrease the amount of stigma and discrimination by educating people, allowing them to learn more about the disease, more about the people that are living with it. It’s devastating the impact of the disease that it has on people, and this is a great way to reach out to them.

Kristine Alarcon, MPH:
Thank you so much for all your efforts. Be sure to join us on our next episode of “Journey to the Cure.” Just wanted to thank Maureen again for all of her time and all of her efforts in conveying such wonderful information around the world.

If Hepatitis B Is Sexually Transmitted, How Come My Partner Isn’t Infected?

Image courtesy of Canva

I thought hepatitis B was sexually transmitted? I just tested positive, but my partner tested negative, we’ve been together for years, what gives?

This question is a common one. Hepatitis B can be transmitted sexually, so why do some people — who were not vaccinated — never get hepatitis B from their sexual partners?

It comes down to factors, such as the type of sexual activity partners engage in, the viral load (HBV DNA) of the infected partner, and who is on the receiving end of infectious body fluids, especially blood (which contains the most virus), and semen.

Having one partner infected, while the other is not, can add more stress to an already traumatic hepatitis B diagnosis. “It was very confusing and made me question how was it possible I was the only one infected,” said a woman who tested positive while her husband tested negative. “I thought it was possibly a mistake, maybe I was a biological anomaly, which of course I was not.”

Let’s look at the factors that may play a role in transmission of hepatitis B infection through sexual activity.

Viral load: Semen, vaginal fluids and blood all contain the hepatitis B virus (HBV), and the higher the viral load in the blood of an infected individual, the more infectious they are considered to be. Having an undetectable viral load might reduce or eliminate the chance of transmitting the virus to someone during unprotected sex; research is still trying to assess whether a person with an undetectable viral load in the blood is able to transmit the virus through sex. This is a good reason for individuals living with hepatitis B to talk to their doctor about the benefits of starting antivirals if they have detectable HBV viral load in their blood; treatment which lowers the viral load in the blood might also serve as a prevention measure for transmitting the virus.

Once an individual tests positive for hepatitis B surface antigen (HBsAg), they should encourage their partners to get screened for hepatitis B, and vaccinated if they are still susceptible to the virus.

The timing of sexual activity: An infected person who is menstruating is more likely to transmit hepatitis B infection to an unvaccinated partner, because menstrual blood can contain higher levels of HBV than vaginal secretions. That is why dental dams and condoms are recommended to provide a reasonable barrier against exposure, during that time of the month.

The type of sexual activity: Certain sexual activities are far more efficient at transmitting hepatitis B virus than others. Oral sex appears to have a lower rate of hepatitis B transmission than vaginal sex. Anal sex carries a higher risk of transmission because of tears in the skin that can occur during penetration, which increases the likelihood of transmission of HBV to an unvaccinated partner.

Fingering carries a lesser risk, unless the infected partner is menstruating while the other partner has bruises or cuts on their hands that could allow entry of hepatitis B virus from the body fluid into the bloodstream. In such cases, gloves are highly recommended.

The hepatitis B status of the other partner: The “uninfected” partner could have already been infected and cleared the virus, or vaccinated as an infant. When a person is first diagnosed with hepatitis B, doctors often test his or her partner for only the hepatitis B surface antigen (HBsAg), which indicates a current hepatitis B infection. If they are negative for HBsAg, they are advised to receive the hepatitis B vaccine as soon as possible. However, this does not mean that they were never infected.

Testing for the hepatitis B surface antibody (also known as anti-HBs or HBsAb), and hepatitis B core antibody (HBcAb) is the only way to identify a past recovered infection or prior vaccination.

Hepatitis B is often called the “silent” infection because many people who get hepatitis B may not experience any of the alarming symptoms (like fever or jaundice). As a result, many individuals may never realize they were infected. A partner who tested negative for HBsAg, may actually have been infected in the past and cleared the infection and now has protective hepatitis B surface antibodies to forever safeguard them from infection. If they’re vaccinated without proper screening, then tested for HBsAb after vaccination, they will test positive for surface antibodies, without ever knowing that their antibodies resulted from a past infection, not immunization.

Bottom line, if one partner is diagnosed with hepatitis B and the other is not, it might seem unusual, but it is not uncommon. Just like any other virus, there is not a 100% chance of transmission with exposure. The undiagnosed partner should get tested using the 3-panel blood test (HBsAg, HBsAb, and HBcAb) and immediately vaccinated if they are still vulnerable to a hepatitis B infection (HBsAb negative).

The is safe, effective, and provides lifelong protection.

Take a quiz to find out how much you know about hepatitis B transmission: click here.

Journey to the Cure: What do I do if I’m pregnant and have hep B? ft. Maureen Kamischke

Welcome to “Journey to the Cure.” This is a web series that chronicles the progress at the Hepatitis B Foundation and Baruch S. Blumberg Institute towards finding the cure for hepatitis B.

In the third episode (part 1), Kristine Alarcon, MPH sits down with Maureen Kamischke, Hepatitis B Foundation Social Media Manager, to discuss what expectant mothers can do when they have hepatitis B.

For any questions about hepatitis B, please email info@hepb.org.

The Hepatitis B Foundation is a national nonprofit organization dedicated to finding a cure and improving the lives of those affected by hepatitis B worldwide through research, education and patient advocacy. Visit us at www.hepb.org, on Facebook at www.facebook.com/hepbfoundation, on Twitter at @hepbfoundation, and our Blog at www.hepb.org/blog

Disclaimer: The information provided in this video is not intended to serve as medical advice or endorsement of any product. The Hepatitis B Foundation strongly recommends each person discuss this information and their questions with a qualified health care provider.

Edited:
Kristine Alarcon, MPH

Special thanks:
Samantha Young

Music:
Modern – iMovie Library Collection

May 19 is National Hepatitis Testing Day

May is Hepatitis Awareness Month and Saturday, May 19this National Hepatitis Testing Day in the United States. This day is an opportunity to increase awareness and testing for both hepatitis B and C. It is also a reminder for health care providers and the public of the importance of testing for viral hepatitis.

Why is hepatitis B testing necessary? Hepatitis B is largely asymptomatic, which means that symptoms don’t always occur or are not obvious. Some people will not know that they have hepatitis B until it is too late, or they may learn of their infection from a blood donation screening or lab work.  There are groups of people who have a greater risk of hepatitis B compared to others, so it doesn’t hurt to be sure. here are some places around the world that have an extremely high hepatitis B prevalence (where many people are infected). It is important that people who are at high risk for a hepatitis B infection see a doctor to get tested, to find out if they have a hepatitis B infection. People living with chronic hepatitis B should be monitored regularly and appropriately screened for liver cancer. So, if you find you do have hepatitis B, talk to your doctor about what to do next.

Remember, hepatitis B does not discriminate. Don’t wait for symptoms. B sure. B tested. If you do not have hepatitis B, then give yourself lifelong protection with the hepatitis B vaccine. The hepatitis B vaccine is safe and effective. Children or adults can get the 3-shot vaccine series, and there isa newly approved two-dose adult vaccine to protect us against hepatitis B! However, the vaccine doesn’t work if you are already infected.

Don’t forget to check out these free, confidential hepatitis screenings this weekend! Check out Hep B United’s resource to find local events in your area. You can also visit the CDC’s website for more ideas on how to increase awareness on National Hepatitis Testing Day, and every day!

Hepatitis Victoria’s “Little Hep B” Hero Book

Hepatitis Victoria in Melbourne, Australia recently released their “bright, colorful, positive and silly” children’s book, Little Hep B Hero! In addition to creating a book, Hepatitis Victoria also created an animation.

Little Hep B Hero, which is available in English, Simplified Chinese and Vietnamese, gives children and their families a delightful glimpse into a young girl’s visit to her neighbor and friend, Rosa. As Rosa and the young girl prepare food and lemonade together, Rosa tells her about living with chronic hepatitis B. Rosa explains what the liver does, what hepatitis B is, how the virus is transmitted, how she maintains a healthy lifestyle with chronic hepatitis B, and shares tips on preventing hepatitis B transmission. Little Hep B Hero also provides cute and easy to understand visuals of the little girl as a superhero while Rosa explains this information.

The book does an excellent job of explaining liver functions and what the hepatitis B virus does to the liver! The analogy of using a sieve to demonstrate how the liver filters toxins in the body was creative. The book also does a great job of indirectly tackling some myths associated with hepatitis B. For example, people are often hesitant to share meals with those living with chronic hepatitis B. Little Hep B Hero lets its audience know that you cannot get hepatitis B through food preparation or sharing a meal, so Rosa cooks a meal for her neighbors.

Little Hep B Hero is an important read for future generations and their families! Getting the conversation started early about hepatitis B will address the stigma and discrimination associated with it. When children are talking about hepatitis B and are knowledgeable about it, hepatitis B isn’t a scary topic anymore. The message of hepatitis B as a family matter highlights the importance of educating and testing family members.

For more information, check out their press release, and to purchase Little Hep B Hero, visit Hepatitis Victoria’s website here.

Journey to the Cure: What Programs are Available for People Living with Hepatitis B?

Welcome to “Journey to the Cure.” This is a web series that chronicles the progress at the Hepatitis B Foundation and Baruch S. Blumberg Institute towards finding the cure for hepatitis B.

In the second episode (part 2), Kristine Alarcon, MPH sits down with Chari Cohen, DrPH, MPH, Vice President of Public Health Programs of the Hepatitis B Foundation, to talk about public health research at the Hepatitis B Foundation.

For any questions about hepatitis B, please email info@hepb.org.

Disclaimer: The information provided in this audio post is not intended to serve as medical advice of endorsement of any product. The Hepatitis B Foundation strongly recommends each person discuss this information and their questions with a qualified health care provider.

Edited by:
Kristine Alarcon, MPH and Samantha Young

Music:
Modern – iMovie Library Collection

Script:

Welcome to Journey to the Cure! Every month, we’ll sit down with scientists from the Hepatitis B Foundation and the Baruch S. Blumberg Institute to talk to you about hepatitis B and efforts to find a cure for hepatitis B. There’s still a long way to go, but we’re here to walk you through our journey.

Kristine Alarcon, MPH:
In our last episode, Dr. Block was talking about how the Hep B Foundation is dedicated to public health research. Can you tell us more about that?

Chari Cohen, DrPH, MPH:
One of our major goals is to get everyone in the United States – or in the world really – but primarily in the US, everyone who has hepatitis B should be aware of their diagnosis and should be able to access to care. In order to do that, we have to do research. We have to figure out what are the best ways to get people tested and into care. In order to do that, we have to first figure out why people aren’t getting tested now, what barriers are people facing, what challenges are people facing to get tested, and how can we help them overcome those challenges. Every time we do a public health program, we are also doing research, so we are collecting a lot of data. And then, we use the data to develop new programs, and we share it with others as well. We also collect information and data on prevalence, so looking at where some of the high risk and highly impacted communities are in the U.S. We will do testing ourselves. We’ll go into communities in Philadelphia, and we’ll do hepatitis B testing. Through that, we know which communities need more care.

Kristine Alarcon, MPH:
What types of public health programs are you carrying out right now?

Chari Cohen, DrPH, MPH:
We have a number of different programs right now. One is our Hep B United Philadelphia program, where we like to train the trainers. In Philadelphia, we’re training people who do health education; we’re training community leaders; and we’re helping them to learn about hep B, so that that they can go into high risk communities and teach other people about hep B. We’re also screening a lot of people. This year, we screened a little over 200 people for hepatitis B. When we find people to be infected, we link them into care. We’re also working on a new project, looking at the challenges that African immigrants face in the US in terms of hepatitis B testing. We’re trying to figure out what are the best ways to overcome those challenges and what are the best ways to get people tested and into care. And then, we have our #justB program, which is our national patient storytelling program, where people who have hep B or with family members who have hep B tell their stories and make videos, and they share how hep B has impacted their lives.

Kristine Alarcon, MPH:
Thank you so much for joining us in this episode!

Chari Cohen, DrPH, MPH:
Thank you!

What Do I Do if I’m a Hepatitis B Vaccine Non-Responder?

Image courtesy of Pixabay

Approximately 5-10% of people do not develop protective antibodies following the completion of the hepatitis B vaccine series.  This is confirmed with a blood test called an anti-HBs titer test which is given 4 weeks following the completion of the series. If the test shows the titer is less then 10 mIU/mL the general recommendation is to complete the series again using a different brand of vaccine (e.g. if you received Engerix B, the first time, switch to Recombivax the 2nd time or vice-versa).  A person is considered to be a “non-responder” if they have completed 2 full vaccination series’ without producing adequate protective antibodies.

Another vaccine option is the new two-dose hepatitis B vaccine, HEPLISAV-BTM. The new vaccine is expected to increase immunization rates for adults in the United States and is administered over a one-month period. The vaccine provides greater seroprotection, which can mean a greater antibody response especially in adults who may be older, obese or live with type 2 diabetes making it an effective vaccine option.

It is also possible that a person who does not respond to the vaccine may already be infected with hepatitis B. Therefore, testing for the presence of the hepatitis B virus (hepatitis B surface antigen or HBsAg) is recommended before diagnosing a person as a “vaccine non-responder.”

CDC Recommendations for Hepatitis B Vaccine Non-Responders

  • Persons who do not respond to the primary hepatitis B vaccine series (i.e., anti-HBs <10 mIU/mL) should complete a second 3-dose vaccine series or be evaluated to determine if they are HBsAg-positive. Persons who do not respond to an initial 3-dose vaccine series have a 30%–50% chance of responding to a second 3-dose series.
  • Revaccinated persons should be retested at the completion of the second vaccine series, 1-2 months following the last shot of the series.
  • Persons exposed to HBsAg-positive blood or body fluids who are known not to have responded to a primary vaccine series should receive a single dose of hepatitis B immunoglobulin (HBIG) and restart the hepatitis B vaccine series with the first dose of the hepatitis B vaccine as soon as possible after exposure. Alternatively, they should receive two doses of HBIG, one dose as soon as possible after exposure, and the second dose 1 month later.
  • The option of administering one dose of HBIG and restarting the vaccine series is preferred for non-responders who did not complete a second 3-dose vaccine series.
  • For persons who previously completed a second vaccine series but failed to respond, two doses of HBIG are preferred.

Hepatitis B vaccine “non-responders” who test negative for hepatitis B infection are at risk for being infected and should be counseled regarding how to prevent a hepatitis B infection and to seek immediate medical care to receive a dose of hepatitis B immunoglobulin (HBIG) if they have been exposed to potentially infected blood.

“Non-responders” who test negative for hepatitis B infection as well as friends and family members should practice ways to prevent the spread of hepatitis B, including washing hands, using condoms during sex, avoid direct contact with blood and bodily fluids, and more.

Hepatitis B vaccine “non-responders” to vaccination who test positive for hepatitis B infection should be counseled regarding how to prevent transmitting the hepatitis B virus to others and the need for regular medical care and monitoring for their chronic infection.

In the case of possible exposures to HBV infected blood or body fluids, it is recommended that non-responders receive 2 doses of hepatitis B immunoglobulin (HBIG) – the first dose should be given within 24 hours of the exposure, and the second dose should be given 1 month later.  The CDC has recommendations online for what to do in case a susceptible person is possibly exposed to the hepatitis B virus.

Check out our previous post on the topic here.

References:

CDC Guidance for Evaluating Health-Care Personnel for Hepatitis B Virus Protection and for Administering Postexposure Management. Retrieved from: https://www.cdc.gov/mmwr/preview/mmwrhtml/rr6210a1.htm

HEPLISAV-B. Retrieved from: https://heplisavb.com/

Hepatitis B Precautions for People Living with Diabetes

 

March 27th is Diabetes Alert Day!

Diabetes is a chronic condition that is characterized by high glucose (or sugar) levels in the blood. It usually occurs when a person cannot produce enough insulin, a hormone that controls blood sugar levels. According to the World Health Organization (WHO), global prevalence of diabetes is on the rise! In 1980, diabetes prevalence in adults over the age of 18 was 4.7%. The number rose to 8.5% in 2014 and continues to increase. In 2015, there was an estimated 1.6 million deaths that were attributed to diabetes.

Like hepatitis B, there have been several studies that show a strong link between type II diabetes and liver cancer. Diabetes and hepatitis B can be a dangerous combination and can work together to increase someone’s risk of developing liver cancer.

Since the hepatitis B virus can be transmitted via blood or other bodily fluids, people living with diabetes are at an increased risk of contracting hepatitis B. In fact, one study found that people living with diabetes between the ages of 23-59 have an approximately two-fold increased risk of hep B infection compared to those without diabetes. According to the Centers for Disease Control and Prevention (CDC), there have been hepatitis B outbreaks in nursing homes, assisted living, and long-term care facilities among people living with diabetes. Some risks for transmission include:

  • Sharing glucose meters between residents without cleaning and disinfecting between uses
  • Lack of proper hand hygiene and failure to wear gloves between fingerstick procedures
  • Using the same fingerstick devices for more than one resident
  • Cross-contamination of clean supplies with contaminated blood glucose monitoring equipment used by home health agencies
  • Sharing injection equipment such as an insulin pen or syringe for more than one person
  • Failure to perform proper sterilization and separating contaminated and clean podiatry equipment
  • Failure to perform proper disinfection between podiatry patients

So, what can you do if you are living with diabetes to prevent hepatitis B transmission?

  • Get tested! A simple three-part blood test will tell you if you have hepatitis B, were exposed, or are protected.
  • Get vaccinated – If you find that you are not protected or if you have not finished your hepatitis B vaccine series. The CDC and Advisory Committee on Immunization Practices (ACIP) recommend that adults between 19-59 years of age living with diabetes get vaccinated to protect against hepatitis B. Those 60-years-old or older should ask their doctor about the vaccine before getting it.
  • Do not share your diabetes care equipment to prevent exposure!

For more information about hepatitis B and diabetes, WHO, CDC, and/or American Diabetes Association. For a personal account of hepatitis B and diabetes, visit Martha Zimmer’s blog post. You can also visit our website for information about diabetes and liver cancer