PPSCC is extremely rare and it has been described in very few case reports. Pathogenesis of PPSCC is actually unknown, because of its extreme rarity [4]. Some authors suggest that chronic pleural inflammation could be one of the causes of PPSCC [1]. The participation of chronic inflammation in the pathogenesis of this tumor is also suggested by the fact that some of the reported cases occurred in patients with empyema cavity with pleurocutaneous fistula [5]; with extrapleural pneumothorax, without fistula, for treatment of tuberculosis [5]; with tuberculosis [6]; and with bronchopleural fistula due to bronchiectasis [7]. In our case, the presence of a big pulmonary bulla with chronic inflammation in the vicinity of the tumor may have promoted neoplastic changes in the adjacent pleura with the final result of squamous cell carcinoma. There are no specific symptoms in PPSCC and the tumor is usually detected on CT or Positron Emission Tomography-Computed Tomography(PET-CT). Preoperative biopsy, especially transthoracic Tru-Cut needle biopsy, is instrumental for the diagnosis of pleural tumors, but the reported rate of accurate diagnosis is not satisfactory [3]. The differential diagnosis of the present case included localized mesothelioma, primary or secondary chest wall tumors, pleural metastasis, and thymic carcinoma. Pleura-based tumor spread was indeed reminiscent of mesothelioma; however, diffuse expression of p40 and p63 and negative expression of WT1, Calretinin and D2-40 ruled out this possibility[4, 8, 9]. Primary chest wall tumors arise from muscle, fat, blood vessel, nerve sheath, cartilage, or bone of the chest wall; nevertheless, postoperative histopathological report revealed squamous cell carcinoma, which also precluded that possibility. Due to no history of tumor and the lack of radiological evidence of tumor involvement of the lung, mediastinum, head, neck and abdomen, secondary chest wall tumors and pleural metastasis were excluded. Although most thymic carcinoma takes the form of squamous cell carcinoma, the current tumor did not involve the mediastinum and lacked expression of c-kit, a highly sensitive marker for thymic carcinoma [8].
Surgical resection is the treatment of choice for localized tumors [4]. The two patients reported by Rüttner et al. were surgically treated and were free of disease 3 and 5 years after the operation [5]. The patient described by Prabhakar et al. died from massive hemorrhage five month after resection, and local or distance recurrence could not be ruled out because necropsy was not performed [7]. A patient with extensive PPSCC was treated with nivolumab after six cycles of cisplatinum and docetaxel and local radiation therapy. Although there was some tumor response, the tumor progressed locally and distantly and the patient died two year after diagnosis [10]. Finally, Yoshida et al. reported on a 33-year-old female with no history of inflammatory disease or smoking who presented with an extensive PPSCC that had a deficiency of SMARCB1 (INI1), a tumor-suppressor gene, the loss which has been associated with malignant tumors of the kidney, gastrointestinal tract, pancreas and uterus. Although intensively treated with chemotherapy, the patient died 10 months after diagnosis [8]. The evidence is scarce, but radiotherapy after complete resection may improve the prognosis of this disease, and this was the rationale followed with our patient.