Clinical improvement in respiratory function in patients with cystic fibrosis (CF) has been reported following treatment with antitumourous chemotherapy.^1,2 It has been suggested that long term upregulation of genes encoding proteins promoting multidrug resistance (MDR), including MDR P glycoprotein, may complement a function of the CFTR protein which is deficient in CF and may be the mechanism by which macrolides exert their effect in CF.^1,3 Previous reports suggested an increase in MDR following chemotherapy in CF patients and called for more reporting of cases of CF patients undergoing chemotherapy.²

We report a case of a male CF patient (homozygous ΔF508), aged 7 years, who underwent chemotherapy for acute myeloid leukaemia. He remained well during six months of treatment, with no chest exacerbations. After cessation of treatment, nasal potential difference measurements showed a 6 mV response with a low chloride perfusion, unusual in CF, with typical CF baseline and Δ amiloride readings (−49 mV and 39 mV respectively). No increase in MDR P glycoprotein mRNA was detected from nasal brushings, compared to three control CF subjects. Six months post-chemotherapy, he remained clinically well, with good lung function (FEV₁ (96%) and FVC (110%); pretreatment FEV₁ and FVC both 60%).

Interpretation of these data is clearly limited by a lack of pre-chemotherapy data. In order that the potential effect of these drugs can be understood, we suggest a formal protocol for collection of quantitative data from cases of CF patients presenting with malignancies, both before and after the initiation of chemotherapy. In addition to records of clinical status, as performed by previous groups,^1,2 we recommend: (a) pre- and post-treatment sweat tests (chloride and sodium values); (b) collection of nasal or (opportunistically) bronchial brushings for quantification of MDR P glycoprotein mRNA, by real time RT-PCR; and (c) nasal potential difference measurements. If the role of MDR proteins in mediating this effect is further substantiated in future CF patients receiving chemotherapy, there may be a role for the development of novel drugs which modulate MDR proteins.