The Diagnostic Pitfalls of Metastatic Merkel Cell Carcinoma: A Case Study
Small blue cell tumors often have diagnostic pitfalls due to their anaplastic nature and morphology. Immunohistochemical
stains play a vital role in their diagnosis.
Merkel cell carcinoma is a rare, neuroendocrine or small blue cell, form of skin cancer. It usually manifests itself as a painless
lump on sun-exposed areas of the body. Merkel cell carcinoma tends to occur in white, older males (60-80 years old). It is
an aggressive tumor that has a tendency to metastasize to lymph nodes and other body parts. Treatment includes
surgery, radiation and/or chemotherapy, depending on the stage of the disease.
Cytologically, it appears as small, uniform round cells with scant to no cytoplasm with nuclei that mold to one another. The
chromatin is finely granular, and there may be a small nucleolus present. Crush artifact is often noted (Fig. 1).
Clinical History/Findings
A 27 year old Latin-American man presented at Parkland Hospital with a firm 6.0 cm enlarging soft tissue mass of the left
arm.
Cytologic Evaluation
The IHC results did not support the diagnosis made in Mexico of rhabdomyosarcoma (Table I).
The diagnosis of Merkel Cell carcinoma in this case was difficult for several reasons. First, the patient was diagnosed as
having a small blue cell tumor at Parkland then returned to Mexico where he was misdiagnosed with
rhabdomyosarcoma and treated. After returning to Parkland Hospital, the tumor continued to increase in size and the
pathologists’ evaluation continued to follow the path of a sarcoma until immunohistochemistry
ruled out that it was not a rhabdomyosarcoma.
Second, the clinical manifestation of the tumor was not consistent with a Merkel Cell carcinoma, which usually appears as a
pink or purple nodule in the head and neck region. These tumors also occur more frequently in the elderly. This tumor
occurred as a growing mass in an extremity of a young man. Rhabdomyosarcomas are the most common soft tissue
tumor in children or adolescents and typically present as growing masses in the head and neck region, and less commonly
in the extremities. Clinically, a sarcoma made more sense.
Finally, the very nature of a Merkel Cell tumor, that is, any small blue cell tumor, is lack of differentiation. Small blue cell
tumors often times require immunohistochemistry to help differentiate between them. The immunophenotype of the
tumor and the morphology of the tumor cells helped to rule out a rhabdomyosarcoma. The specific dot-like pattern of
the cytokeratin stain (Fig. 5) performed in December of 2005, along with the complete immunophenotype and
cytomorphology, assisted in the final diagnosis of Merkel Cell carcinoma (Table II).
Conclusion
This case illustrates that the clinical picture does not always correlate with the true nature and cytomorphology of the
tumor. The tumor in this case clinically presented itself as a soft-tissue tumor such as a sarcoma, but the cytomorphology
and the immunophenotype proved otherwise. The fact that this tumor had been previously diagnosed in Mexico as a
rhabdomyosarcoma and the patient given subsequent treatment emphasizes the importance of adjunct testing, such as
immunohistochemistry.
Submitted by:
Winona Miller, Senior Cytotechnology Student
Lansing School of Nursing and Health Sciences, Bellarmine University
Courtesy of Parkland Health and Hospital System, Dallas, TX
Small blue cell tumors often have diagnostic pitfalls due to their anaplastic nature and morphology. Immunohistochemical
stains play a vital role in their diagnosis.
Merkel cell carcinoma is a rare, neuroendocrine or small blue cell, form of skin cancer. It usually manifests itself as a painless
lump on sun-exposed areas of the body. Merkel cell carcinoma tends to occur in white, older males (60-80 years old). It is
an aggressive tumor that has a tendency to metastasize to lymph nodes and other body parts. Treatment includes
surgery, radiation and/or chemotherapy, depending on the stage of the disease.
Cytologically, it appears as small, uniform round cells with scant to no cytoplasm with nuclei that mold to one another. The
chromatin is finely granular, and there may be a small nucleolus present. Crush artifact is often noted (Fig. 1).
Clinical History/Findings
A 27 year old Latin-American man presented at Parkland Hospital with a firm 6.0 cm enlarging soft tissue mass of the left
arm.
Cytologic Evaluation
The IHC results did not support the diagnosis made in Mexico of rhabdomyosarcoma (Table I).
The diagnosis of Merkel Cell carcinoma in this case was difficult for several reasons. First, the patient was diagnosed as
having a small blue cell tumor at Parkland then returned to Mexico where he was misdiagnosed with
rhabdomyosarcoma and treated. After returning to Parkland Hospital, the tumor continued to increase in size and the
pathologists’ evaluation continued to follow the path of a sarcoma until immunohistochemistry
ruled out that it was not a rhabdomyosarcoma.
Second, the clinical manifestation of the tumor was not consistent with a Merkel Cell carcinoma, which usually appears as a
pink or purple nodule in the head and neck region. These tumors also occur more frequently in the elderly. This tumor
occurred as a growing mass in an extremity of a young man. Rhabdomyosarcomas are the most common soft tissue
tumor in children or adolescents and typically present as growing masses in the head and neck region, and less commonly
in the extremities. Clinically, a sarcoma made more sense.
Finally, the very nature of a Merkel Cell tumor, that is, any small blue cell tumor, is lack of differentiation. Small blue cell
tumors often times require immunohistochemistry to help differentiate between them. The immunophenotype of the
tumor and the morphology of the tumor cells helped to rule out a rhabdomyosarcoma. The specific dot-like pattern of
the cytokeratin stain (Fig. 5) performed in December of 2005, along with the complete immunophenotype and
cytomorphology, assisted in the final diagnosis of Merkel Cell carcinoma (Table II).
Conclusion
This case illustrates that the clinical picture does not always correlate with the true nature and cytomorphology of the
tumor. The tumor in this case clinically presented itself as a soft-tissue tumor such as a sarcoma, but the cytomorphology
and the immunophenotype proved otherwise. The fact that this tumor had been previously diagnosed in Mexico as a
rhabdomyosarcoma and the patient given subsequent treatment emphasizes the importance of adjunct testing, such as
immunohistochemistry.
Submitted by:
Winona Miller, Senior Cytotechnology Student
Lansing School of Nursing and Health Sciences, Bellarmine University
Courtesy of Parkland Health and Hospital System, Dallas, TX
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| The Texas Society of Cytology |
Figure 1: Fine Needle Aspiration biopsy (FNAB) was performed. A
diagnosis of a high grade malignant neoplasm comprised of small blue cells was
rendered. The patient returned to their home country where a second
biopsy was performed and a diagnosis of embryonic rhabdomyosarcoma was
rendered. The patient received 3 cycles of chemotherapy and then returned
to Parkland Hospital for additional treatment.
diagnosis of a high grade malignant neoplasm comprised of small blue cells was
rendered. The patient returned to their home country where a second
biopsy was performed and a diagnosis of embryonic rhabdomyosarcoma was
rendered. The patient received 3 cycles of chemotherapy and then returned
to Parkland Hospital for additional treatment.
Figure 2: Before resuming treatment, a core biopsy and touch preps of
the left forearm showed a malignant neoplasm consistent with a high grade
sarcoma.
the left forearm showed a malignant neoplasm consistent with a high grade
sarcoma.
Figure 3: AE1-AE3 Positive Staining 40X
Figure 4: CD56 Positive Staining 40X
Figure 5: CK20 Positive Staining in Dot-Like Pattern
Figure 6: Chromogranin Positive Staining 40X
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Table 1