The rate of leukaemia (blood cancer) in young children in the polluted Durban suburb of Merebank appears to be 24 times higher than in other parts of the country.
And the rate of other childhood cancers in Merebank and elsewhere in south Durban also appears to be unusually high.
These are some of the startling results of a Mercury survey analysed by public health specialist Duane Blaauw, of the University of Natal's Nelson Mandela Medical School.
He says the evidence pointing to a cancer cluster in Merebank is not a fluke result, and needs to be investigated thoroughly by officials.
The aim of the six-week survey and investigation by The Mercury was to examine claims by citizen groups that the rate of cancer might be higher than normal on the Bluff, in Wentworth, Austerville and Merebank.
Several residents fear that industrial air pollution is killing children and adults or making them sick - a claim which is denied strongly by local fuel refineries and other south Durban industrial companies.
Industries acknowledge that air pollution in the area is a problem, but they suggest it is a "nuisance" issue rather than a health menace.
Two of the biggest polluters in south Durban - the Engen and Sapref refineries - also believe they are being singled out for undue focus when there is evidence that many smaller companies, motor traffic exhaust fumes and indoor pollution add significant burdens.
However, because of serious information shortfalls in South Africa's cancer, health and air pollution records, The Mercury had to resort to its own door-to-door and telephone research, and look for answers in other countries.
Basic details of at least 60 reported cancer cases in three parts of south Durban were collected over six weeks, but these are likely to form a small proportion of the total.
But in four days in the small suburb of Merebank alone, The Mercury tracked down 11 recent cases of cancer in young children. Only these childhood cases have been analysed so far, because they are not complicated by old age or other cancer factors such as tobacco-smoking, alcohol or prolonged exposure to sunlight.
After comparing these cases with national cancer statistics over the past 10 years, Dr Blaauw calculated that the rate of leukaemia in Merebank children under the age of 10 was at least 24 times higher than the national average.
The rate of all other cancers in this age group was more than four times higher than the national rate.
Dr Blaauw, who has also worked at the National Cancer Registry in Johannesburg, stressed that anecdotal studies based on a small number of cases should be interpreted with caution. Nevertheless, he said his calculations were conservative and could not easily be dismissed as a fluke or "chance" result.
"The rate of leukaemia in Merebank children seems to be unusually high and should be evaluated by more formal studies."