The objective of the study was to review the natural history of patien
ts with a malignant pleural effusion but without obvious evidence of a
primary. to assess the value of investigations used to look for a pri
mary and to assess the response to palliative chemotherapy. This was d
one by a retrospective study of patients' notes at the Lung Unit, Roya
l Marsden Hospital, Sutton, Surrey. Improvement in tumour-related symp
toms (and duration) on chemotherapy was assessed by the patient before
the first course of chemotherapy and following each course using simp
le descriptive criteria as follows: (I) complete disappearance of symp
toms (CR); (2) good improvement in symptoms (PR); (3) minor or no chan
ge in symptoms (NC); (4) worse symptoms CPD). Pleural effusion objecti
ve response (and duration) according to Hamed definition: success defi
ned as a continued absence of reaccumulation of pleural fluid on all f
ollow-up radiographs; any reaccumulation was regarded as a treatment F
ailure. Overall survival was measured from the date of histological/cy
tological diagnosis to death. The study included 42 patients. 27 males
and 15 females with a median age df 55 years. A primary was found in
15 patients (36%), and considered to be lung cancer. A total of 11/32
(34%) had a thoracic computed tomography (CT) scan with abnormalities
compatible with a diagnosis of lung primary. When thoracic CT scan was
negative, fibre optic bronchoscopy was always negative (0/13). Abdomi
nal and pelvic CT scan, abdominal ultrasound, pelvic ultrasound and ma
mmograms failed to reveal the primary. Twenty-three patients underwent
local treatment and 37 received systemic chemotherapy. A total of 29/
37 (78%) patients achieved symptomatic improvement (median duration. 6
months) and 32/37 (86%) an objective response of their pleural effusi
on on chemotherapy (median duration, 6 months). The median survival of
the whole group was 12 months (3-60+ months). In this series the thor
acic CT led to a diagnosis of lung primary in 34% of the cases. Other
radiological examinations and bronchoscopy were unhelpful. Chemotherap
y achieved symptom relief in 75% of patients.