In this case report the histological findings of the first biopsies gave three potential differential diagnoses: ACC, PLGA and BCA. The basaloid appearance of the tissue would have been characteristic for ACC but the low proliferation index demonstrated with MIB1 immunohistochemical staining gave no support to this diagnosis. The appearance and location in the tongue base would have been unusual for PLGA. Nevertheless, immunohistochemistry and low proliferation index could have been consistent with this diagnosis. An adenoma with a predominant differentiation of basal cells was considered as a third differential diagnosis. No definite tumour invasion could be assessed microscopically. Therefore, no histological evidence of a malignancy could be confirmed as the key determining factor in establishing the malignant nature of a salivary gland tumour is the demonstration of an infiltrative margin. However, this is known to be more difficult in biopsies where it may not be possible to obtain a precise diagnosis.3
In this case, immunohistochemical stainings were unhelpful and did not differentiate between the differential diagnoses named above. The possible diagnosis of basal cell adenocarcinoma (BCAC) was not considered, although it is well documented that neither immunohistochemical methods nor ultrastructural characteristics do distinguish between BCAC and BCA.4
However, even though no tumour invasion could be demonstrated, the clinical presentation was that of a malignant tumour. The general consensus at the multidisciplinary team meeting was strongly in favour of malignant disease. The tumour had grown rapidly, was painful and completely occluding the pharynx requiring an emergency tracheostomy. The enlarged cervical lymph nodes and the nodular opacity in the left lung were suggestive of metastatic disease. The size of the tumour, measuring more than 4 cm in diameter, indicated a high clinical stage of tumour. Although tumour grading was not available, a poor outcome was suggested considering the relative importance of stage versus grade in minor salivary gland tumours.5
Treatment options were discussed and surgery would have been the preferred approach if the patient's health and fitness had allowed. Alternatively, radiotherapy was considered based on evidence from previous studies6
of patients receiving radiotherapy alone for minor salivary gland carcinomas. These demonstrated long-term local tumour control especially in patients unfit for surgery. In this case, as the clinical findings had much improved without starting any treatment, the decision was made to observe and follow the patient up at regular intervals.
When the first biopsies were taken, a surgical trauma occurred that might have led to a change in blood supply resulting in tumour necrosis. This represents one of many mechanisms thought to be responsible for spontaneous remission of cancer.7
In 1935 spontaneous regression of a carcinoma of the tongue after biopsy was reported by David Roxburgh.8
However, without a confirmed histological diagnosis of malignancy, our case did not fulfil the strict criteria of spontaneous regression of a cancer defined by Everson and Cole in 1956. They postulated spontaneous regression of cancer to be a partial or complete disappearance of a malignant tumour in the absence of all treatment, or in the presence of treatment that is considered inadequate to exert a significant influence on neoplastic disease.9
In our case, a second attempt to biopsy the lesion was unsuccessful and no further tissues samples were taken at the postmortem examination; hence, the exact nature of the tumour, as well as the mechanism leading to its regression, remain uncertain. Histological distinction between benign and malignant basaloid neoplastic proliferations of the salivary glands is difficult and may, ultimately, rely on the demonstration of an infiltrative growth pattern or perineural invasion.
- Difficulties in establishing a histological diagnosis from fragmented biopsies.
- Immunohistochemical stainings may not be helpful in differentiating between benign and malignant minor salivary tumours.
- The process of taking a biopsy may alter blood supply to a tumour and may contribute to tumour regression.