What sampling technique yields few cells and a relatively great amount of contamination, making it less effective in the diagnosis of neoplasia?

The technique that yields few cells alongside a relatively high level of contamination, thereby making it less effective for diagnosing neoplasia, is impression smear. This method involves pressing a slide against a lesion to collect cells, which can lead to a limited amount of cellular material.

Due to the nature of the sampling, impression smears can easily pick up a considerable amount of background debris, tissue, or contaminants that do not originate from the lesion itself. This excess contamination complicates the interpretation of the sample, making it harder to identify cellular changes indicating neoplastic processes. The limited number of cells collected further reduces the likelihood of obtaining a representative sample of the neoplastic population, which is critical for accurate diagnosis.

In contrast, other sampling techniques, such as fine needle biopsy, brush cytology, and cell scraping, generally allow for the acquisition of more cells and less contamination, providing clearer insights into potential neoplastic changes.