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Between 1935 and 2001, many studies have appeared in the literature from different parts of the world on bone marrow invasion by solid tumours.1–4 After lymphoma, the primary tumours that most frequently involve the bone marrow are malignancies of the prostate, breast, lungs, thyroid, kidney, and stomach.4 Metastatic deposits of malignant melanoma have also been described.3 In many instances, primary tumours remain clinically undetected and are identified only at necropsy.1
The value of bone marrow aspiration in the diagnosis of malignant neoplasms was confirmed when four of eight cases of malignant melanoma were found to harbour tumour deposits in the bone marrow.3 In a series of 57 patients with known carcinoma of the prostate, five had carcinoma cells in the bone marrow, with no other diagnostic evidence of skeletal system involvement.2 The usefulness of such a comparatively simple procedure is emphasised by studies of large series of patients with known malignancies,2,3 especially when the primary tumour is known to have a predilection for the skeletal system.
The patients in the abovementioned studies had known primary tumours and at present bone marrow aspiration/biopsy is routinely performed for staging of tumours, but the high incidence of metastatic deposits found in these bone marrows2–4 emphasises the practicability of routine bone marrow aspiration in patients with suspected malignancy or severe anaemia. It is difficult to determine from the literature the incidence of malignant cells in routine series of unselected bone marrow aspirates, so we investigated the usefulness of routine bone marrow examination for the diagnosis of malignancies.
A one year prospective study covering the year 2001 was conducted in the department of pathology, Government Medical College, Srinagar, Kashmir, India. The bone marrow smears were routinely stained by Leishman’s stain and Perl’s reaction. Periodic acid Schiff and Sudan black stain were used as and when required. Of the 318 bone marrow samples studied during the year 2001, eight cases contained metastatic deposits. All of the patients in our present study had pallor (anaemia) as one of the main symptoms, and underwent bone marrow aspiration to determine which type of anaemia they were suffering from. In patients with metastatic deposits the normal haemopoietic cells of the bone marrow are replaced by tumour cells, resulting in myelopathesic anaemia, and later on they are liable to develop myeloid metaplasia and myelofibrosis. In most of the cases, the bone marrow was difficult to aspirate, especially in cases of epithelial cell deposits, with mostly cancerous cells obtained in a background of peripheral blood—a fact that has already been reported.4
After leukaemia, lymphoma most commonly involves the bone marrow and almost 10% of cases of lymphoma invade the bone marrow. In our present study, lymphoma (non-Hodgkin lymphoma) made up a quarter (two cases) of all the secondary tumours of the bone marrow, along with neuroblastoma (two cases)—a childhood tumour. Neuroblastoma, non-Hodgkin lymphoma, and acute lymphoblastic leukaemia pose a considerable amount of difficulty in diagnosis because all three are round cell tumours with a very similar morphological appearance. In acute lymphoblastic leukaemia, the peripheral blood film examination is of paramount importance because it shows the presence of lymphoblasts, whereas neuroblastoma cells in bone marrow smears tend to form rosettes and may show neural or neurofibrillary differentiation. Non-Hodgkin lymphoma is thought of as a malignancy of old age, although it can be seen at any age; however, childhood lymphomas are mostly of high grade.
In most studies, the incidence of tumour deposits in the bone marrow from gastrointestinal tumours was low, but they made up a quarter of the cases presented here (two cases). This could be explained by the low number of cases in our study, together with the high incidence of gastrointestinal cancers, especially of the oesophagus and stomach, seen in Kashmir.5 Deposits from prostate and breast tumours (one case each) are known to have a predilection for skeletal metastasis.
Finally, several features worthy of comment are that the metastatic tumour cells are easily identified in the bone marrow smears because they look foreign within the native bone marrow cell population. These cells are usually identified in groups, even at low power examination, because they are larger than most of the bone marrow cells. Single cells are more difficult to recognise, although they never resemble the normal bone marrow cells. The primary site of the malignant deposits may be extremely difficult to determine on a morphological basis only, but their origin can sometimes be inferred from their morphological appearance, especially in mucous producing carcinoma, squamous carcinoma, some adenocarcinomas, and in many cases of metastatic neuroblastoma or melanoma.