Hugo Chavez's US 'cancer plot' put to the numbers test

By Ruth Alexander BBC News

 
Venezuelan president Hugo Chavez had a cancerous tumour removed in 2011

Venezuelan President Hugo Chavez speculated last month that the US might have used a secret weapon to give Latin American leaders cancer, as the number of them with the disease was "difficult to explain using the laws of probabilities" - but is it?

"Would it be strange if they had developed the technology to induce cancer and nobody knew about it?" Mr Chavez asked in a televised speech to soldiers at an army base.
Treated for cancer himself last year, he was speaking the day after the Argentinian President Cristina Fernandez de Kirchner was diagnosed with the condition - or misdiagnosed, as it turned out.
Brazilian President Dilma Rousseff, 64, had treatment for lymphoma in 2009.
Her predecessor, Lula da Silva, 66, has been treated for throat cancer.
Paraguayan President Fernando Lugo, 60, was diagnosed with lymphoma in August 2010 but is now in remission after chemotherapy.
'Disease of the elderly'
This made five leaders out of a total of 24 Latin American countries, at the time of Mr Chavez's speech, although it became clear after an operation this month that President Fernandez was suffering from something else entirely.

Latin American leaders and cancer

• Argentine President Cristina de Kirchner: underwent surgery for thyroid cancer in January 2012 but it was found to be a misdiagnosis
• Former Brazilian President Luiz Inacio Lula da Silva was diagnosed with throat cancer in October 2011 - doctors say the 66-year-old is responding well to chemotherapy and should make a full recovery
• Venezuelan president Hugo Chavez flew to Cuba in June 2011 to have a cancerous tumour removed - he says he has made a full recovery, but never disclosed what kind of cancer he was suffering from
• Paraguayan President Fernando Lugo was diagnosed with lymphoma cancer in August 2010 but is now in remission after chemotherapy
• Brazil's president Dilma Rousseff received treatment for lymphoma cancer in 2009 and has fully recovered

President Chavez stressed that he was thinking aloud rather than making "rash accusations". The US State Department described his comments as "horrific and reprehensible".

But was he right that such a concentration of cancer is statistically improbable?
Cancer is a very common disease, points out Eduardo Cazap, an Argentinian doctor and the president of the Union of International Cancer Control, based in Geneva.
Over a whole lifetime, the risk of cancer is around one in three for women and one in two for men.
At any one time it affects about 1% of the world's population.
In the case of the Latin American leaders, Dr Cazap says, their risk is higher than that of the general population because they are all in their 50s and 60s. Cancer is a "disease of the elderly", he points out.
Another issue to consider is the fact that the Latin American leaders were not diagnosed with cancer in the same year, but over a three-year period.
So, if we make a specific adjustment for the age group of the population and then multiply by three, five out of 24 - roughly one in five - is not a very unexpected number, Dr Cazap says.
Cancer increase
It is worth noting that not all the leaders were diagnosed with cancer while in office - former Brazilian president Mr da Silva discovered he had throat cancer in the year after he stepped down.

With Courtesy of BBC