Cytology of lumps and bumps (Proceedings) - Veterinary Healthcare


Cytology of lumps and bumps (Proceedings)


Malignant epithelial neoplasms

Squamous cell carcinoma

Squamous cell carcinomas are malignant neoplasms arising from the superficial epithelium of the skin. They are often superficially ulcerated which results in secondary superficial bacterial contamination and inflammation. It is therefore important that samples are collected from the center of the mass as well as the surface.

The cells of squamous cell carcinoma are large with angular cytoplasmic margins. The cytoplasm often has a "glassy" or smooth appearance due to the presence of keratin. Cytoplasmic keratohyalin droplets may also be present. Nuclei are usually round and centrally located and there is often marked chromatin clumping, a feature of malignancy. Other features of malignancy include marked variation in cell size, nuclear size, and nuclear/cytoplasmic ratios. Often nuclei appear too immature for the degree of cytoplasmic keratinization.


Adenocarcinomas of the skin include apocrine gland adenocarcinomas (sweat gland adenocarcinomas) and mammary adenocarcinomas. Most skin adenocarcinomas are specifically classified as to type primarily on the basis of location.

Adenocarcinomas are formed of rafts and clusters of round cells with basophilic cytoplasm and round nuclei. At least some of the cells contain numerous or single cytoplasmic vacuoles which represent a secretory product. Some cells are so filled with secretion that the nuclei are pushed peripherally; these are termed signet ring cells. Adenocarcinoma cells usually fulfill numerous malignant criteria including variable nuclear size, variable nuclear/cytoplasmic ratios, multiple nucleoli, large irregular nucleoli, and abnormally clumped chromatin.

Malignant Connective Tissue Neoplasms


Hemangiopericytomas are spindle cell tumors of low-grade malignancy that appear to arise from the pericytes surrounding small vessels. They tend to be locally recurrent and invasive but do not metastasize until late.

Cytologically, aspirates from hemangiopericytomas are quite cellular for a spindle cell tumor. Tumor cells are plump with wispy cytoplasm and often indistinct cell margins. Nuclei are centrally located and round to oval. Nuclear atypia is generally minimal to mild unless the tumor is particularly aggressive. Because of their close association with blood vessels, distinct capillaries may be prominent in aspirates.


Fibrosarcomas are generally more cellular than their benign counterpart, the fibroma. Cells are usually larger, more basophilic, and plump. Nuclei are round to oval and exhibit significant malignant criteria.


Liposarcoma is a relatively rare spindle cell tumor of the skin. It is a typical spindle cell neoplasm in general morphology and is distinguished primarily by the presence of numerous large unstained vacuoles in the cytoplasm of a number of cells. These vacuoles contain fat.


Melanomas of the skin may be either benign or malignant. Cytologic morphology is less important in determining malignancy than is location of the tumor. Melanomas of the mouth and distal extremities have greater potential for malignancy than those of the trunk.

Cytologically, melanomas are characterized as having a mixture of round cells and spindle cells. The distinguishing feature of these cells is the presence of black cytoplasmic granules. The degree of pigmentation varies from tumor to tumor and even among cells within the same tumor. Degree of pigmentation does not necessarily correlate with degree of malignancy. In most cases of malignant melanoma nuclei will fulfill criteria of malignancy; however, if the cells are heavily pigmented these criteria may be obscured.

Discrete cell tumors


Histiocytomas typically occur in young dogs (less than three years old) and are benign. These tumors typically ulcerate and spontaneously regress. Histiocytomas in older dogs should be regarded as potentially malignant as they may progress to a disseminated form (malignant histiocytosis).

The cytologic appearance of histiocytomas in young dogs is variable depending upon their stage. Prior to ulceration aspirates are relatively hypocellular and contain a uniform round to oval cells with eccentric nuclei and fairly abundant pink to bluish cytoplasm. Nuclei have the appearance of typical macrophage nuclei and generally do not fulfill malignant criteria. Following ulceration, aspirates are more cellular and include a significant inflammatory infiltrate. At this stage the morphology closely resembles that of chronic inflammation only and one must rely on the combination of history, cytology, and gross appearance to make the proper diagnosis.


Click here