Cancer is first discovered during about 1 in every 1000 pregnancies. Of these cancers diagnosed during pregnancy about 1 in 20 is a non-Hodgkin lymphoma (NHL).
This means that NHL appearing during pregnancy is extremely uncommon. As a result of this, the relatively small number of women in this situation has made it difficult to produce absolutely reliable statistics.
NHL is not a single disease but includes a number of cancers, which behave very differently.
The description and classification of the various types of NHL has developed over the years as more has been learnt both about the immune system and the cancers themselves. The most recent classification still recognises the difference between Hodgkin lymphoma and NHL but then goes on to divide NHL into some fifteen different tumour types.
From a practical viewpoint doctors divide all these various types of NHL into one of three groups: low grade, intermediate grade or high grade. This division is based on the appearances under the microscope and helps predict how the condition will behave.
Low grade NHLs usually have a relatively slow growth rate, running a long course and often needing little or no treatment for months or possibly years. When they do need treatment they respond well but are likely to come back again at some time in the future. They frequently respond to treatment on several occasions over the years but may eventually become resistant or transform to a high grade form of NHL.
High grade types of NHL usually grow more rapidly and behave more aggressively and so need prompt treatment. Despite this they are more likely to be completely cured than low grade NHLs. Around half of all people with high grade forms of NHL will be cured by the use of intensive chemotherapy.
Intermediate types of NHL lie somewhere between these two extremes in their behaviour.
The research evidence from the studies that have been done over the years suggest that when NHL appears during pregnancy it is almost always one of the high grade types of the disease and so is a more rapidly growing and aggressive form of NHL. This does not mean that the cancer behaves any differently from similar types of high grade NHL in people who are not pregnant but does mean that low grade, slower growing types of NHL are very rare during pregnancy.
The figures also show that NHL diagnosed during pregnancy is likely to be more advanced and have spread further than would normally be the case. This is probably because the presence of pregnancy often leads to some delay in making the diagnosis and, as the tumours are usually quite rapidly growing, then even a short delay gives more time for them to spread.
A final difference during pregnancy is that normally NHL most commonly affects the lymph glands but in pregnancy it is often found in organs like the breast, the ovaries and the womb. This may be because of the hormonal changes and alterations to the pattern of blood flow that take place during pregnancy making these organs more likely to be affected.
Older reports suggested a generally poor outcome when NHL was discovered during pregnancy but over the years the results of treatment of the more aggressive, high grade, forms of NHL have improved dramatically and this improvement appears to apply to pregnant women as well as other patients.