Fine-needle aspiration of tumors is another approach that is widely used. It involves aspiration of cells from a mass, followed by cytologic examination of the cells after they have been spread out on a slide. This procedure is used most commonly with readily palpable lesions affecting the breast, thyroid gland, lymph nodes, and salivary glands. Modern imaging techniques permit extension of the method to deeper structures, such as the liver, pancreas, and pelvic lymph nodes. Use of this diagnostic modality obviates surgery and its attendant risks. Although it entails some difficulties, such as small sample size and sampling errors, in experienced hands it can be reliable, rapid, and useful.
Cytologic (Papanicolaou) smears provide another method for the detection of cancer. Historically, this approach has been used widely for discovery of carcinoma of the cervix, often at an in situ stage, but now it is used to investigate many other forms of suspected malignancy, such as endometrial carcinoma, bronchogenic carcinoma, bladder and prostate tumors, and gastric carcinomas; for the identification of tumor cells in abdominal, pleural, joint, and cerebrospinal fluids; and, less commonly, for evaluation of other forms of neoplasia. Neoplastic cells are less cohesive than others and are therefore shed into fluids or secretions (
Fig. 6.35 ). The shed cells are evaluated for features of anaplasia indicative of their origin from a tumor. The
Fig. 6.35 (A)NormalPapanicolaousmearfromtheuterinecervix.Large,flatcellswithsmallnucleiaretypical.(B)Abnormalsmearcontainingasheetofmalignantcellswithlargehyperchromaticnuclei.Nuclearpleomorphismisevident,andonecellisinmitosis.Afewinterspersedneutrophils,muchsmallerinsizeandwithcompact,lobatenuclei,areseen.(Courtesy of Dr. Richard M. DeMay, Department of Pathology, University of Chicago, Chicago, Illinois.) gratifying control of cervical cancer is the best testament to the value of the cytologic method.
Immunohistochemistry offers a powerful adjunct to routine histologic examination. Detection of cytokeratin by stains performed with specific monoclonal antibodies points to a diagnosis of undifferentiated carcinoma rather than large cell lymphoma. Similarly, detection of prostate-specific antigen (PSA) in metastatic deposits by immunohistochemical staining allows definitive diagnosis of a primary tumor in the prostate gland. Immunocytochemical detection of estrogen receptors allows prognostication and directs therapeutic intervention in breast cancers.
Flow cytometry is used routinely in the classification of leukemias and lymphomas. In this method, fluorescently labeled antibodies against cell surface molecules and differentiation antigens are used to obtain the phenotype of malignant cells (Chapter 12).